@viragomann:
There's no need for advanced options to pushing routes. This is done by "Local Networks" option.
The idea to put a route in server advance config comes from this guide.
It makes the difference, without that route I cannot access internal subnet with the user who has client specific overrides.
The client configuration was ok since the beginning, a route print from windows command line shows it knows how to reach 192.168.1.0/24, the IPv4 Local network of the client specific override.
Don't know how to check the routes on firewall: it can reach 192.168.5.0/28, the Ipv4 tunnel network configured with OpenVpn server, but I suspect it has no route to 192.168.6.0/28, Ipv4 tunnel network of the client specific override. Adding that route manually traffic flows as expected.