Disk Quota calculation

In hosting controller, we should be able to change the disk quota behavior.
 
Currently, the disk quota seams to add both Allocated disk space and email (maybe more, but this is all I’m using).
 
In our case, I want to allocate a maximum of 1Gb of Space on the web server and 500Mb on the mail server. Currently, I can’t do this, I have to assign 1.5Gb to my hosting plan and then set 500Mb for my email.
 
I suggest that each server had its own quota (Web separated from e-mail, etc.) I know that database is already separated.
 
Maybe an option should be added to either have a Global disk space setting or to have the limit by servers.
 
Thank you!