I've been trying to figure this out

[HellSniper]

All hitboxes are virutally the same size and position, relative to the ground position. Think of GunZ as a XYZ-based 3D Object:

http://vignette2.wikia.nocookie.net/...20130906181334

Gunz Hitboxes are literal boxes. Meaning, their position moves with the actor they are associated with. Actions that actors do, for example, lunge, is a static invisible location in which any hitbox that enters will trigger. This is why when you elunge, the lunge action is in a different position than your hitbox. Melee shots do not follow the same logic and are assigned to the hitbox.

Heres a screenshot with the developer overlay active

The red cylinder is either the hitbox/collision box.