How can we improve WHMCS?

It would be great if we have an option to send domain expiry notices based on the expiry dates instead of the due dates since it's related to the expiration of the domain, not if the invoice has been paid or not.

I know there is an option to sync expiry and due dates but it's not a solution here since we have some clients who pay their invoices annually so we need to send the expiry notice even if the due date is different.