So far I've found out that changing the below options will completely restrict player XP gain.
-Turning off AIM ASSIST (why is this crap necessary?)
-Turning off AIM ASSIST ZOOM SNAP
-Turning off SPECTATING SQUAD SPAWN
-Turning off SQUAD SPAWN TYPE (even disabling squad spawn to make it harder)
-Turning on MIXED SQUADS ALLOWED (the standard coop mode allows AI in your squad so I dont know why this ruins it for Portals)
-Changing MAN-DOWN TYPE (its funny seeing everyone crawling, and they can be executed still)
-Changing REINFORCEMENT MULTIPLIER (for longer or shorter games)
Lets be honest though, altering ANYTHING besides the map, player count, and enabling basic *** default AI will completely restrict XP and its just stupid. I know that this will never even be looked at by the devs, but I just wanted to state the need for this to be addressed as you give us something that's supposed to be full of fun but its just an empty box of toys without the joy of progression.