Arrows and thrown weapons usually don't fly straight, except maybe on the first few meters. Their flight trajectory resembles an arc due to gravity. That is real physics. That's why you have to adjust your aim depending on where you are in relationship to your enemy.

You are on level ground: Aim a bit higher to compensate.
You are on higher ground: Aim at or a bit lower at the target.
You are on lower ground: Aim much higher then the target.