filter traffic from ovpn-server

when i try and set up a firewall rule to filter on traffic cming from my open-vpn server,
I am offered

  in-interface=<ovpn-username>

only, ie interfaces one per user.

Is there no way to simply say

  in-interface=ovpn-server
or
  in-interface=all-ovpn-server

to to this once for all users?