RE: SHOOTING HIGH OR LOW FROM TREESTAND?
Most of why your confused is miscommunication.
If you use proper form out of a treestand and bend at the waist, you aim for the exit hole. This has a tendency to be slightly (slightly) higher than from level ground ONLY because of the path of travel for your arrrow, again, aim for the exit hole.
People who simply lower their bow arm without bending at the waist will tend to shoot HIGH. That is why most people overshoot deer. (not to mention them reacting to sound). For those people who DO NOT bend at the waist, they have to aim lower than they expect to hit. I find that crazy, why not just use proper form and take the guess work out.
The other reason to aim lower than normal would be for laser range finding your distance. If you shoot the distance with your range finder to the deer from the tree and it reads 26 yards, the actual distance is more like 25 yards from the ground level. One might, might aim slightly lower but, if you know that knowledge ahead of time and range it for 26 yards, subtract that one yard, bend at the waist, pick a hair that puts your arrow through the deer for the correct pass though shot for the exit hole and nail it.
I never aim low in anticipation to the reaction of the whitetail. I learned that lesson and will never do it again. I aimed just below the heart and a very nervous buck at 41 yards, My arrow hit exactly where I was aiming and flew just under the heart of the buck, he did not drop in reaction, had I aimed at the top of the heart, he'd be on my wall today.
If you must aim low, make sure you are still in the vitals.