Question BatchRendererGroup properties override approach

Hello Everyone,

I'm trying to learn how BatchRendererGroup passes properties to the Shader when drawing a batch.

from what I understood (please correct me if I'm wrong)

BatchRendererGroup uses a large global compute buffer that contains 128 Shader Properties per instance even though it uses a single Shader Property.

My question is:

EG: let's say we have 10 spheres and 10 squares that survived the frustum culling, Normally 2 draw calls will be requested.

How does BatchRendererGroup pass these properties to the shader using a single global compute buffer ?
to be more precise how to get the correct Batch/Instance index in Global Compute Buffer from the shader ?

Thank you in advance!