Take the following diagram:

. E .
X X .
X X .
X X .
X X .
. A .

Considering the Attacker has line of effect (like an arrow slit) to the Enemy. According to RC pg 219 on determining cover, lines along the edges of an obstacle aren't blocked. Therefore, the Attacker has only two lines blocked (the two corners on the left side of the enemy square) since the right side corners' lines are along the edges of the obstacle (with one on top of the other).

In that case the target will have only partial cover???

EDIT: For comparison, in the diagram situation below (still with an arrow slit between them) the target will definitely have superior cover.

. E .
. A .

EDIT2: I increased the blocked terrain to be more visual, consider it a arrow slit tunnel.

EDIT3: To make it even clearer, assuming corners are numbered clockwise.

 1 2
. E .
 4 3 

In the second case the lines to all corners are blocked (giving it superior cover). In the first case line to 1 and 4 are definetely blocked, and lines to 2 and 3 overlap, that would make it have partial cover by the rules, but both situations are pretty much alike unless cover is affect by "peeking on the side". Am I right in that thought?

EDIT 4: New diagrams to further clarify the matter:

Diagram 1      Diagram 2  
. . . . | .    . . . . | .
.A. . . [E.    .A. . . [E.
. . . . . .    . . . . | .

This | is a wall, and this [ is an arrow slit, they both sit on the edge of squares. I know they are assimetrical in relation to defense (meaning the Enemy has cover and the Attacker doesn't). The point I'm making is: in BOTH cases we have an enemy behind an arrow slit, but in the first case, since the wall ends after the arrow slit, the enemy would have ONLY partial cover, instead of superior cover that I expected.

  • \$\begingroup\$ I'm feeling stupid, are the X's blocking terrain, and the dots open space, or are the dots walls and the X's open space? 4th edit clarified it for me. thanks. \$\endgroup\$ – GMNoob Oct 25 '11 at 11:04
  • \$\begingroup\$ The X's are blocked terrain the .'s are open terrain. I'm assuming the X's have some sort of small tunnel that gives line of effect from the Attacker to the Enemy. And in the last diagram |'s are wall that are blocked, and ]'s are arrow slits that block but still gives line of effect. \$\endgroup\$ – Luiz Borges Oct 25 '11 at 11:07
  • \$\begingroup\$ This question is similar to my own rpg.stackexchange.com/questions/5719/… \$\endgroup\$ – Adriano Varoli Piazza Oct 25 '11 at 14:53
  • \$\begingroup\$ Yes, actually I've seem your question before I made mine. My doubt here is in the case of an arrow slit that is not on a continous wall (like the Diagram 1). Do the elbows and feet peeking out the side like GMNoob says justify partial cover instead of superior cover?? \$\endgroup\$ – Luiz Borges Oct 25 '11 at 18:24
  • \$\begingroup\$ If some part of the body is not in cover from the attacker, it's "partial" by definition, no? \$\endgroup\$ – GMNoob Oct 25 '11 at 19:02

No, they are not the same.

Your question quotes the rules extensively and you seem to understand them and have interpreted them correctly so I won't bother going over them further.

The real question you seem to have is "Why do the rules treat these two situations identically when I consider them to be very similar?"

With your first diagram, both parties have equal protection. The game rules assign that situation as "cover".

The problem is that an arrow slit is a specific asymmetrical defensive measure. They are designed so that the person on one side can fire ranged weapons with as few restrictions as possible while maintaining a great deal of protection.

While a person directly on the other side may have some protection, it should be distinctly less. In game terms, the person on the protected side has "Superior Cover" while the enemy has none.

You can find many images of arrow slits on the net, here is one example. There is plenty of room for the defender to pick his spot and get a good shot while leaving very little of himself exposed. Compare to the two enemies trying to shoot each other around two corners. They are both going to be peeking around the corner, looking for a good shot. They will have significantly less cover to protect themselves with.

  • \$\begingroup\$ I do understand how arrow slits are supposed to work (and they are mentioned on RC on constructed terrain). My doubt is exactly that, are they picking around the corner? I remade the diagrams using wall and arrowslits. \$\endgroup\$ – Luiz Borges Oct 25 '11 at 10:57
  • 1
    \$\begingroup\$ Yes, elbows and feet are likely to be peeking out of the side, especially assuming that combatants are always in motion. (which DnD asssumes) Never build an arrow slit defense on the edge of a wall :P \$\endgroup\$ – GMNoob Oct 25 '11 at 11:07
  • \$\begingroup\$ That was what I assumed, I just find it odd that this happens... then again, I consider DnD4e world to be based on non-euclidian geometry, and I'm pretty sure R'lyeh is somewhere in this world. \$\endgroup\$ – Luiz Borges Oct 25 '11 at 18:20
  • \$\begingroup\$ Yes, that is why there is a blog called Square Fireballs :) \$\endgroup\$ – GMNoob Oct 25 '11 at 19:01

You pick one square and determine cover based on that. You would choose the most advantageous square.

In this case each is the same. 2 lines are blocked and two are not so you just have regular cover instead of superior cover. If 1 line is blocked you have cover, if 3 or more are blocked you have superior cover.

To answer your edit specifically You choose the point with the fewest lines blocked to the enemy's square. Thus for your first case you chose either point on the right side (point 2 or 3) and they only have 2 lines blocked each so only grant cover. Your second example is definitely superior.

  • \$\begingroup\$ I get that, the problem is that in comparison with the second diagram the situation is not all that different (both have only an arrow slit to target). Therefore both should have the same cover, unless in the first case there is some peeking in the corner that helps?!?! \$\endgroup\$ – Luiz Borges Oct 25 '11 at 2:10
  • \$\begingroup\$ If its not a solid wall then both cases are identical. \$\endgroup\$ – wax eagle Oct 25 '11 at 2:21
  • \$\begingroup\$ That's my point, it is a solid wall, remember that the X is blocking terrain and the line of effect is only granted by an arrow slit. In the first case at least two corners are to be blocked for cover, and in the second all of the four corners are blocked for cover. Since the type of blocking terrain and the line of effect are identical in both, my question is: in the first case it is partial or superior cover? \$\endgroup\$ – Luiz Borges Oct 25 '11 at 2:30
  • \$\begingroup\$ The first case is partial. You pick the square with the most open lines so in this case you either take point 2 or point 3 and it has 2 lines open. Points 1 and 4 are irrelevant here as they have more than 2 lines blocked and you always take the fewest lines. wizards.com/dndinsider/compendium/… \$\endgroup\$ – wax eagle Oct 25 '11 at 3:20

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