Distance is not the issue.

The issue is the difference in angle between the arrows flight path and gravity. On level ground, gravity is acting perpendicularto the arrows flight path. From an elevated postion, this angle becomesless and reduces gravity's effect.

For a demo, hold a limber fishing rod straight level and note the bend caused by gravity. Hold the rod downward (or upward)at any appreciableangle and the bend will be less.

This is why you must hold under on uphill as well as downhill shots. Pythagoras will get you close buthe won't help you undestand what's happening to your arrow in flight and this clever Greek'serror grows larger at steeper angles.