Maybe because I don't think the Call of Duty games have a 'moderate' option? it's either open or closed. Also perhaps the individual games nat settings are effected by the ports you have forwarded. For instance if you have forwarded the ports for Call of Duty you could have a open nat on that game, but closed on Crysis 2.
Crysis 2 requires you to forward ports
TCP 80, 443
UDP 3658
To be able to play comfortably from behind a firewall. Hope that helps.