Hey (I realized it was an off day a bit late ),
In these playgrounds there are 3 impostors, sphere, box and compoundBody. The position of the compound body is the center of mass. If I move it up you can see the center is at the top of the head.
See this playground: https://www.babylonjs-playground.com/#492ZK0#9
So to setup the collision I would:
- set the position of the visual mesh
- position the collider meshes (eg. box and sphere) around the visual mesh
- position where you want the center of mass (compound body)
- add collider meshes as a child of the compound body
- create physics imposters
Let me know if Im not making sense, hope this helps.