How can we improve WHMCS?

Hi WHMCS,

We want to charge our billing per inbox, for example, we might have a client setup 3 inboxes, one uses 0.1GB storage, second uses 1.2GB storage, and third uses 0.5GB storage.

Total would be 1.8GB storage used.

We would like to charge $1/GB per inbox, but we can only see a way to setup billing as a cumulative GB amount across all inboxes...
Not per inbox amount, please consider adding this to future releases.

Thanks