Yea, using 5 makes it hard to boost, and if you leave your main account out, because you used it to refer all your additional accounts, non of them will get 3x XP. Also, using a 70 on your main account will make non of them get 3x XP as well, until they get within 8 levels(not positive but its around there). Your best bet is to not use one of the refered accounts if you want to boost.