Report for Application Size per Client

Dear Community,
I need a report at the beginning of each month for the sum of the "Application Size", independent of "Application Type" and "SubClient", of Clients within a "Client Group" from the previous month.
I have tried to find out the information using the report "Backup job summary", but I only get the sizes per job and not per client.

Which report can I use to map my requirements?
Can someone help me?

Thanks a lot!