Thank you for your feedback
The reason why I’m using a dedicated proxy server (non of the UCS systems) is simple. All externally available web-pages/systems are using port 443. Means I can map this port (without a revers-proxy) just to one web-page/system.
In my setup, the proxy is taking all 443 requests and depending on the requested side/service - it will be forwarded to system A or system B. I’m sure there are also other solutions possible - and I’m happy to learn 
With the proxy conf from UCS I’m not yet happy. I hope I can find something else - just copy and past was not working - even if I changed the IPs (and coms looks like as being just http instead of https).
As mentioned before - I’m IT pro - but not in this area (linux based systems).
If someone has a nicer config - please let me know. The basic functions (mail) are also working with the simple config above.