Throwing overhand

Overhand, 3/4 and sidearm are relative to how much the body leans. If the arm drops below the plane of the shoulders you'll tend to lose velocity. If you try to throw overhand with the body upright, shoulders level to the ground, you'll probably lose velocity. JMO but I believe that having the arm just above the plane of the shoulders at release is probably optimum for most pitchers for velocity. Most pitchers lean a bit so that ends up being around 3/4. Some pitchers lean a lot and end up throwing over the top even though the arm isn't far above the plane of their shoulders at release.

It may be foolish to bring them into it but the people from set(not amateur) probably have some pretty good information on something like this.