Relay IP and Direct IP one firewall, two PCs


I have two PCs behind the same firewall each running Unite (one is Vista and one is XP). I have a single network set up in Unite and both PCs log in with their own, separate Comodo user accounts which are both members of the same Unite network. One PC gets a direct IP connection every time the other gets a relay IP connection every time. I can only guess that this is because of NAT or something similar on the firewall that they share. Is there a configuration item I can change in one of the PCs so that they don’t have to both try to use the same ports for Unite (if that is the problem), perhaps in the config.ini or the config-server.ini files so that they can both get direct IPs?

port forward on router.