What constitutes the most protective degree of cover?

Question

The rules for cover state:

If a target is behind multiple sources of cover, only the most protective degree of cover applies

In most situations, determining which cover is most protective is fairly straightforward. Against almost all attacks, the order of protectiveness is half < three-quarters < total. What I want to know is whether that is the only way to interpret the 'most protective cover' statement. To give a concrete example of a situation where this might be relevant, let us look at fireball.

In this question on fireball ignoring total cover, it is established that fireball can ignore total cover by going around corners. However, the spell description does not explicitly say that the target does not gain a bonus from cover for the saving throw, as sacred flame does. This means a target with three-quarters cover but not total cover could possibly get the +5 bonus to their Dexterity saving throw.

If a target has total cover and three-quarters cover, and is exposed to fireball going around a corner, the +5 to the Dexterity saving throw provided by three-quarters cover would be more protective than the no benefit provided by total cover.

This is just an example, so let's not get too caught up in the details of it (it may not even work like I have put it, but that is not the thrust of the question).

What I really want to know is:

If a target has total cover and three-quarters cover, and a situation arises where the benefits of three-quarters cover would be more beneficial than the benefits of total cover, does the target get the benefits of three-quarters cover or total cover?

Answer 1

There is no case where 3/4 cover applies and full cover doesn't.

The first two paragraphs talk a lot about what constitutes cover, but there are two lines in particular that are relevant here.

A target can benefit from cover only when an attack or other effect originates on the opposite side of the cover.

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For example, if a target is behind a creature that gives half cover and a tree trunk that gives three-quarters cover, the target has three-quarters cover.

The first of these establishes when you get cover. Specifically, it establishes that "cover" isn't a status effect or a state that a character can be in, "cover" is a benefit gained against a particular attack. There's no concept of a character "being in cover" as a character state, they only gain the benefit of being behind cover as part of an attack.

To put it another way, you are not under cover unless you are actively being attacked by a source that comes from the opposite side of a physical barrier.

The second line tells us how to apply multiple sources of cover that apply at the same time. Basically, you find the largest physical barrier between the source and the target, and apply that level of cover. If you have a waist-high wall that would give half cover and a head-high wall that would give total cover between you and the source of the attack, then you have total cover.

From these two lines, we get an order of operations for how to apply cover. When determining cover, you have to ask three questions:

1. Is there a significant object between the source and the target?
2. Does the source effect have the ability to bypass certain obstacles?
3. What is the biggest object between the source and the target?

For Fireball, the rules are pretty clear about what happens with the partial cover/full cover combo: Since fireball travels around corners, as long as it has an unobstructed path to you, you don't get the benefits of cover. Since neither of the walls actually block any of the flames from getting to you, you don't benefit from either of them. It spreads over the top of a waist-high wall just as easily as it spreads around a head-high wall.

If the cover is not in between the source and target, it doesn't count. If the cover is in between the source and the target, it counts. If a spell effect has the ability to effectively come from a different direction than the expected source, like how a Fireball can round corners, then that ability has to apply equally to all kinds of cover. Cover doesn't count unless it actually interposes between source and target.

Or, to quote Jeremy Crawford, Your cover is foiled if an effect spreads around it and reaches you.

Answer 2

Three-quarters cover applies, not total cover

Diagram of a potential situation where this question could be applicable:

target   3/4  total  point of origin of ice storm
   O      !     |     .

If we apply two things to the scenario, it becomes nearly clear:

1) Things do what they say they do.

Total cover says [target] can't be targeted directly by an attack or spell, although some spells can reach such a target by including it in an area of effect.

Three-quarters cover says [target] has a +5 bonus to AC and Dexterity saving throws.

Total cover does not say that the target has a +5 bonus to AC and Dex saving throws, so a target benefitting from total cover does not gain those benefits. Similarly, something ignoring total cover does not necessarily ignore three-quarters cover, because it would say so if it did.

2) Specific beats general.

In this question we determine fireball ignores total cover and because of this tweet from Crawford saying "your cover is foiled if an effect spreads around and reaches you", we see that the language "spreads around corners" means "ignores cover".

However, ice storm simply states each creature in the cylinder must make a Dexterity saving throw, being more specific than total cover, and therefore being able to target the creature. It does not use the same "spreads around" language though, so it does not ignore all cover, but the benefits of total cover do not apply.

So?

In the Cover section (PHB 196, emphasis mine):

If a target is behind multiple sources of cover, only the most protective degree of cover applies.

If total cover is not being protective, it is not the most protective degree of cover.

The most protective cover in the case of ice storm is three-quarters, so the benefits of three-quarters cover apply.

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I do not answer about the trebuchet intentionally.

This is because the situation isn't applicable there. The trebuchet was not and could not target you, yes. But when the wall is being destroyed, you're not making a save vs the trebuchet anymore, but the wall, which cannot provide cover versus itself.

Answer 3

In this case, I don't think the total cover would even factor into the equation, because it does not apply.

Imagine, for instance, that a character is facing 3/4 cover with 1/2 cover on his back (maybe he's on a city wall with a safety railing behind him). If a monster tries to shoot this character in the back, only the 1/2 cover will apply, because the 3/4 cover is not actually in the way of the monster's attack.

So, in your Fireball example, you'd examine all the sources of cover the character can use. Say they can't use a source of full cover because the Fireball spell finds a way around it, but there's a source of 3/4 cover the spell cannot get around. Just like in the previous example, you'd only consider the cover that actually impedes the attack.

Additionally, rules-as-written total cover isn't protective at all:

A target with total cover can't be targeted directly by an attack or a spell, although some spells can reach such a target by including it in an area of effect.

There's no mention of a bonus to AC or saving throws. This backs up my suggestion, once you've bypassed the cover it no longer provides any benefit.

Answer 4

They get the most protective cover applicable to the individual effect

Regardless of the edits on the original question, my answer is still the same.

In the original iteration when fireball was cited, you get the benefit of 3/4 cover as it's most protective for your situation assuming that your table views that wrapping around corners doesn't deny you your +5 Dex save bonus. RAW are unclear on that aspect, so it would be a DM decision.

As for the the trebuchet example, you have total cover from the trebuchet's attack and cannot be targeted. That is the most beneficial cover for that specific effect. When the wall is destroyed, though, and rocks come flying back towards you, that is a different effect and you would defer to the cover that is applicable to you at relative that effect.

So if you were simply standing directly behind the wall and it's the wall that you're trying to avoid, then you have no cover relative to it; rocks fall and you might die.

Conversely, were you hiding behind the throne and using it as 3/4 cover, you would get the benefits of that cover for whatever Dex save you need to make; rocks fall and you've a +5 on the save to not die. If you avoided the effect of the wall exploding and the ceiling was made unstable as well, you would not have any cover benefits from it falling down on you unless it was a particularly unusual throne that had some sort of overhang to duck under; rocks fall and you might die.

Although 5e uses turns to describe the passage of time during combat, it does not mean that all activities on a specific turn occur simultaneously. For example, Opportunity Attacks occur just after the activity that triggered them.

Answer 5

'Most Protective' versus 'Highest'

As you said,

The rules for cover state:

If a target is behind multiple sources of cover, only the most protective degree of cover applies

Ultimately summing up your question in bold you said:

If a target has total cover and three-quarters cover, and a situation arises where the benefits of three-quarters cover would be more beneficial than the benefits of total cover, does the target get the benefits of three-quarters cover or total cover?

I would suggest that in the case of cover, where the only benefit we're looking for is protection, you could substitute "beneficial" for "protective," leaving us with:

If [...] three-quarters cover would be more [protective] than [...] total cover, [which degree of cover applies]?

You may notice that last substitution was borrowed straight from the PHB text. In case that doesn't make my answer super obvious, here it is:

If (only) the most protective degree of cover applies, it follows that in any given situation it is the most beneficial cover that applies, regardless of it's level or fraction or whatever.

What is the purpose of the rule?

It can be dangerous to make assumptions about developer intent but if I had to guess, I'd say it seems pretty clear to me that the point of the quoted rules for cover is the word only: if you're behind 1/2 cover and 3/4 cover, you don't get +2 and +3 to your AC/DEX save, rather you get "only the most protective" one.

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Your Examples

Through different edits of the question, you mentioned a fireball example and a trebuchet example. While you asked not to get too hung up on them, for the purposes of clarity and helping others with those exact issues, I'll address them here.

Fireball: As pointed out by V2Blast in the comments, Jeremy Crawford ruled that "Your cover is foiled if an effect spreads around it and reaches you." So this specific example wouldn't be affected by any degree of cover.

Trebuchet: If the weapon is strong enough to destroy a wall, that wall won't provide cover, as described in the PHB; rather it would help a creature hide. If, regardless of lack of visibility, the person aiming the trebuchet managed to hit the right part of the wall, again, the wall would not provide any degree of cover.