Domainmapping working 90% as wanted

I have a multisite network at
I have created a sub-site wich works fine on its own
I want to map in such a way that is still visible in the browser-adressbar. (in the background it should run on
a page like should also be available through

I have full control over 3 Centos 7 VPS with WHM/cPanel. I also have a full-fledged DNS-control and can adjust any DNS-entry needed. (Which ofcourse can also be done with the cPanel-accounts itself.)

I have tried everything (i think) but all that worked was redirecting to which is not the desired outcome.

can you please advice what should work? (alias, addon, redirect, iframe redirect w/e) so that I know what to troubleshoot further?

again: the desired functional level should be: a page like should also be available through

thanks in advance
Alexander Korf