Virtual Server Owner Default

I have been looking everywhere and can’t seem to locate where the default for the virtual server owner’s unix username is configured. I am sure it is painfully simple and I have overlooked something, but if someone could point me in the right direction it would be greatly appreciated.

Virtualmin is generating usernames in the form of domain.tld and I would like it to simply use domain ( ${DOM} vs. ${PREFIX} correct )? HELP!