Anybody can get nat2 with ps3?

Correct me if I'm wrong, believe that NAT 2/3 is dependent on the ports you forward instead of the latency? Weird thing was, was playing SF4 on PS3 with NAT3 and was unable to join/to b joined for online matches, however, when challengers connect up while u r playing in arcade mode, it works fine...... no disconnection nor lag......... strange......