What happens when I dismount my steed after sharing an AoE spell with it?

Question

The spell Spirit Guardians is a 15' AoE spell with a range of Self, and it is a Concentration spell that lasts for 10 minutes. (PHB, 278)

Find Steed includes the following: (PHB, 240)

While mounted on your steed, you can make any spell you cast that targets only you also target your steed.

Regarding spellcasting range, the PHB reads on page 201:

Other spells, such as the shield spell, affect only you. These spells have a range of self.

When multiple spells are in effect, the PHB says on page 206:

Combining Magical Effects

The effects of different spells add together while the durations of those spells overlap. The effects of the same spell cast multiple times don't combine, however. Instead, the most potent effect—such as the highest bonus—from those castings applies while their durations overlap.

For example, if two clerics cast bless on the same target, that character gains the spell’s benefit only once; he or she doesn’t get to roll two bonus dice.

Suppose I am mounted on my steed and I cast an AoE Concentration spell that targets only me, such as Spirit Guardians, and I choose to have it target my steed as well. It looks like creatures surrounding me will notice no difference as the spells effects do not combine, correct?

However, having cast this spell, if I dismount my steed and send it off to another part of the battlefield where our AoEs do not overlap, does the spell still stay in effect for my steed for its duration as long as I hold concentration?

Answer 1

Yes.

From the section on Find Steed that you have quoted, the spell has the same effects on your mount that it does on yourself. There are no further requirements for staying within a certain range of the original cast with a Self-targeting spell.

You spell effects might not stack on nearby enemies, but you can certainly send your steed off as far as they can get in the spell's duration.

Answer 2

Spirit Guardians does not work with find steed.

While mounted on your steed, you can make any spell you cast that targets only you also target your steed.

Spirit Guardians targets you, an area of effect, and creatures that begin their turn in the area of effect. As such it does not work with find steed.

Moreover, this Sage Advice confirms that spells that target self with a parenthetical area of effect don't work with find steed.

Answer 3

Hey I believe this definition of range will come into the solution:

Once a spell is cast it's effects aren't limited by its range, unless the spell description says otherwise (PHB p203).

It is like you are effectively able to cast the self spell at touch range, you do not have to maintain that range once the spell begins.

The other aspect seems to be very carefully worded in the definition of the steed.

You can make any spell you cast that targets only you also target your steed.

Hence for 1 spell, for 1 concentration, you get 2 targets instead of 1. So yes both AoEs should be active around you and your steed, while maintaining concentration.