With those single pin set-ups, I am probably wrong but, I thought a lot of guys try to match the size of the housing to just under the size of the hole in their peep, that way it helps them center everything for the best and most consistent shot. Of course you wouldn't really be able to do that until you had it mounted on the bow and look through your peep now would you LOL. As far as just aesthetics go, a bigger housing means a larger field of view when sighting down range.