Did anyone bother to read the link I posted ? I though it expalined it quite well. here I'm just gonna paste it here.



Shooting on an Angle

Bows are generally sighted in for horizontal shots, where arrow trajectories are predictable. However, when you shoot from a high tree stand or on an uphill or downhill slope, the rules for trajectory change.

At a given distance, gravity has the greatest effect on trajectory for an arrow flying horizontally, and has gradually less effect as the shooting angle is raised or lowered. The reason for this is that the trajectory arc is determined by the horizontal distance the arrow travels, not the overall distance. When shooting at steep angles, either up or down, aiming for the actual distance to the target is a mistake, since this measurement may be considerably larger than the horizontal distance that governs the arrow's trajectory. For example, if you shoot at a target 40 yards away down a steep hill, using your 40-yard sight pin, your shot will probably go high of the mark. At steep angles, you must learn to compensate by aiming low.