This is an interesting question and one that is hard to define in a confined answer.
Fundamentally, however, when a bullet is shot from a rifle at an angle other than horizontal, it will shoot Ravens and buzzards compete with each other for carrion but research suggests this has little effect on numbers high.
Thus, if you are zeroed at 100 yards on level ground and then stalk in the Scottish Highlands and take a shot from a lofty perch at a beast at an acute angle downhill the bullet will shoot higher.
The same is true if a stag was above you at 100 yards and you had to raise the rifle. The shot would still go high. Why is that?
Well, it’s all a matter of geometry and gravity acting on a bullet’s flightpath.
The trajectory is flatter as the angle reduces the horizontal distance the bullet travels to reach the stag and the effect gravity has on it.
Thus, the horizontal distance is correct and not the linear distance, as gravity works perpendicularly to a horizontal line.