ORIGINAL: virginiashadow
Think of the exit hole. If the shot is a really extreme downward angle, such as hunting on the side of a hill with a deer walking below me (treestand already 20 feet high, plus the deer being below me on a hill might put the deer almost 25-28 feet below me), I might aim just a little low. If the shot is an uphill shot, I am a little high. It has always seemed to work for me...
Whether your shooting an extremely downward OR upward shot you should always aim a bit lower. It doesnt seem to make sense to aim low when shooting uphill at first, but the laws of physics guarantee that its true.