You see, your problem is you're thinking TOO much. If you practice it, you'll know. That said, at the heights most people hunt at just treat it like any shot, but you have to maintain form. To do that you have to bend at the waist. Some people say draw aiming straight out and then bend... whatever. At any rate the biggest problem is form, not the difference in distance. If you use a range finder to pre-range objects such as trees, do it straight out parallel to the ground, not pointing at the bases. The downward angle at the shot will take care of the difference in distance. At most you're looking at a couple yards. Practice grasshopper.... don't think. And make sure you practice the 5 and zero yard shot from above. It doesn't matter if it's 10 feet up and you hunt at 20... you'll learn and succeed.