Another thing to remember when shooting from heights is the angle of pass through. It's just like making an adjustment of where you want your arrow to enter from a ground shot when the animal is quartering away. Your "bullseye" so to speak changes with angle. This becomes less of an issue at longer distances but at ranges like 10 to 15 yards and 15-20 feet up in a tree creates a fairly significant angle of entry making for what from the ground would be a double lung winds up being a single lung shot.