Determining Cover for Close and Area Attacks
Like Ranged Attacks: You determine cover for these attacks in the same way as for ranged attacks, with two exceptions:
Origin, Not Attacker: Treat the origin square of the effect as the attacker’s square.
Creatures Aren’t Cover: Creatures don’t provide cover against close and area attacks.
Published in Dungeon Master's Guide, page(s) 43, Rules Compendium, page(s) 220.