I am assuming you mean when will you see a vertical change in impact. You have to think of it in terms of horizontal flight distance not distance to target. Imagine a shot across the street 25yds, now imagine the same shot but you are now on the 80th floor of the Sears tower, still use the 25yd pin, even though flight distance has increased to maybe150yds. The reason being that the arrow is fighting gravity only 25yds still. This example is quite a stretch and may not work out technically but should illustrate the principle. If you are hunting level ground from a 20' elevation you'll never see a reason to change your point of aim. Put that treestand on a hillside and then you may have to account for that. I try to look horizontally to a treetop to get a feel for the true distance. Some people will have problems with form when bending over to make a shot at extreme angles, you must bend at hips to make sure upper body remains unaffected and thus bow remains unaffected, in my opinion this is what causes most accute angle shot problems, not the trajectory. Riflemen in the Rocky Mtn. areas probably need to worry about this more than typical archers do.
