A-----> B -- C <------D
If A fires at B, he gets no cover from C, despite C providing cover to B from A's attack.
If A fires at B, he (B) gets no cover from C, despite C providing cover to B from A's attack.
If A fires at B, he (A) gets no cover from C, despite C providing cover to B from A's attack.
Which of these two interpretations did you mean (if either)?
Not that either of these two interpretations make sense to me with either your diagram or mine.
When attacking at an angle, use your judgement as to when the cover no longer applies.
So, we have no rule on this is what you are saying, which is what I expected.
My original example, although I was not clear on it, was one of PCs C, D, and E shooting at NPC A past PC B who is engaged. How far over would they have to be for PC B to no longer be in the way (i.e. giving cover to NPC A)? I would think that this is a very frequent scenario due to the stickiness of OA in this edition.
Alternatively, NPC A on his turn should be able to position himself to the best location such that he gets cover against as many of C's, D's, and E's ranged attacks from PC B as possible. Granted, PCs C, D, and E could move to eliminate that cover, but in doing so, they are forced to move (which means that they might have to exit the rocks or trees that are giving them cover). PC B on his turn could move to the opposite side of NPC A and then give all of his allies PCs B, C, and D shots at NPC A without penalty. On NPC A's turn, he could then again move to the opposite side of Fighter B, etc.
If the answer is #1 above, then C only has to move a few feet and A no longer has cover from B. This is a bit nonsensical to me. If half cover applies, then moving a couple of feet 50 feet away means that C sees a hair more of A, but B is still significantly in the way. I think I'll go with #2. It makes more sense than #1 (too restrictive) or #3 (too generous) and 60 degrees is easy to judge (having used hexes for years).