If there's 6 in a tank, and two are mated, they will own 2/3 of the tank, and the other 4 will be on the other side.
Usually mated pairs are the only pair in a tank. Most LFS's that I have been to keep them seperated from the other clowns as they have more value being a pair..
Or you could get two smaller clowns, let them decide who gets to be boy / girl and have a mated pair in a year or so..
Mated pairs will usually be of different sizes, accept each other (you may see the male do the "submissive shimmy" to the female), and don't generally fight..
If there are 6 in a tank, and they are captive bred, chances are there aren't mated pairs, and possibly not even pairs yet. Most would be juveniles still..