There seems to be a glitch that sometimes causes Orange to show as 100/100 even though there are actually more people than that in the arena. Earlier tonight a squaddie was trying to get into Orange which showed as 100/100 from the Lobby while Blue was something like 130/200, but I was in Orange and there were actually 153 people in it. It makes it look as though the lesser populated arena has a lower cap.
(That was what I was originally complaining about in the general forum, I just didn't realize it was a glitch and the reported numbers were incorrect.)