Geometry should also come into play here. The pythagorean theory states that in a right triangle the length of the hypotenuse(the shot) is equal to the sum of the squares of the lengths of the legs(distance from ground to target and height). So the distance on ground to target (a) squared and height(b)squared = shot distance (c)squared. So lets say your target is 30 feet (10yds) and height is 30 feet.
30(squared)+30(squared)=c
900 +900=1800 ft
now take the square root of 1800 = 42.43ft
the shot distance is now 14 yds

The higher you go the more dramatic this change is.