For melee, I give combat advantage for flanking, for when the defender doesn't have room to move, when the defender...

For melee, I give combat advantage for flanking, for when the defender doesn't have room to move, when the defender is on the ground, and so on.

Does anyone have any suggestions for situations that give combat advantage for ranged attacks with bows or crossbows? Deft archers are common enough, and deft characters can switch their double positive roll for double damage when they have combat advantage, so combat advantage is important.

Flanking doesn't work with ranged attacks, as it's harder to hit someone who is engaged with an ally in melee, and hitting someone who lie down is probably harder than if they stand up. These situations shouldn't give combat advantage.

Difference in height is one suggestion, for example if you fire down at people from a castle wall. Attacking someone who is unaware might give combat advantage, which enables the sneaking archer that picks off targets.

It would be nice to come up with some more situations that can be used in regular fights, in our case usually indoors in dungeons. Any ideas?