Getting Storage Size by Tenant from a shared index

I have a MT environment where some of my indices are shared between tenants. I need a way to find out the total storage used by each tenant. We use Filtered Alias for tenants for searching , but I cannot figure out a way to get the storage stats for a specific tenant using the alias. The /alias1/_stats endpoint returns data, but that is for the whole index . Is there any other way to get the storage size used by a specific tenant.

Ravi