No further setup is necessary - no state behaviors, no animating viewpoint position, no pose space or other hacks, just root scale. It's not recommended to scale avatar too small (below 0.1 scale) or too big as that might lead to issues with using the menu, similar to extremely tiny ...
All the avatar needs to do is scaleavatar root(not armature, not hips, and not any other bone). No further setup is necessary - no state behaviors, no animating viewpoint position, no pose space or other hacks, just root scale.