During prime time, its really not a problem, cant get in one, go into the other. Off prime time, its a bit different (affects Euro and similiar time zones players more) - but I've never had a problem going into the lesser numbered arena. The cap is what it is.
My squaddies and I will all swap so we are in the same arena - if we cant find a fight, we'll go and start one - up, go to a base, get it flashing - if no one ups - start attacking town/ack guns etc, until we annoy someone into upping.
ymmv,
Wurzel