Ok, I have a fast bow and mine shoots 8" high out of a treestand at 25 ft high. When zeroed at 20 yards from the treestand, I am good from the base of the tree all the way out to 32 yards with one pin. At 32 yards I am 2" low. When I shoot off the ground, zeroed at 20 yards, I am about 5 to 6" low at 30 yards. This is with very lite arrows.
If elevation and gravity pull doesn't change the shot then explain this. Take a rifle place parallel 3 ft off ground, fired a shot. Now take the same rifle 3 ft off the ground still parallel but shooting up a mountian, fire a shot. The bullet shot uphill will impact the ground at a closer distance than then bullet fired on flat ground. Same with a Bow. This happens all the time when us Florida hunters go out west.