Johan it's not the distance to the target it's your point of aim on the animal.

If the animal is standing 90 dgrees to you the point on the animals side that you aim to hit the heart is in direct line with the heart. If the animal is above or below you as in Steve's example or quartering to or away from you in my example and you aim at that point on the animals side that you would have aime for a 90 degree heart shot you are going to miss the heart.

Archers who shoot on 3D targets quickly learn this.