Hi,
yes, the UsdPhysics does contain only the very minimal subset of attributes that are very common. All the other parameters are right now extending the UsdPhysics schema through PhysxSchema additional APIs (you will see them in the property panel).
The documentation can be found here:
http://omniverse-docs.s3-website-us-east-1.amazonaws.com/omni_usd_schema_physics/105.1/index.html
Mentioned here:
http://omniverse-docs.s3-website-us-east-1.amazonaws.com/omni_physics/105.1/extensions/runtime/source/omni.physx/docs/index.html#usd-physics-schema
So what you need is to apply PhysxSchema.PhysxRigidBodyAPI for example and then you have access to all the parameters.
Regards,
Ales