Fixed space quota per user

Granted, I didn't played enough with limits/server plans but from a first impression this is not possible with Virtualmin:

Quota is limited by the total on the home directory and each user can also have its own user quota (under the main /home/user virtual server quota)

But what if someone wants to offer a fixed amount of quota per user? Sure, you can do this on the server templates, set a default quota. Except I could not find any setting to disallow the Virtualmin server user from modifying them.

1. Set a default quota per user, (cannot be changed by the Virtualmin administrator or users)
2. Set a max quota per user (can be changed by the Virtuamin administrator but only set to the max amount allowed)

As for number 2, you could say that they are still limited by the total quota assigned to the virtual server, but that is different. I want to limit quotas for mail accounts. Example, how can you offer email plans if you can't limit them to a fixed or max size per user?

If you give 50 GB virtual server quota but only want to allow 1 GB max email accounts how exactly would you do this today?

Is there a setting for this? Not allow to change the default user quota on a specific plan?