When I shot sights, I always centered the pin in the peep. To me, it doesn't make much sense to center the sight housing in the peep. You have to concentrate on the sight housing and, simultaneously, choose the correct pin and, simlutaneously, choose your aim point and, simultaneously, put the chosen pin on your chosen aim point. That's four things to worry about at the same time! Ignoring the housing and centering the pin in the peep removes at least one of those worries.
Nobody, repeat NOBODY, shooting a multi-pin sight centered the sight housing in the peep until somebody hit the market with a sight that had a round housing. I'm sure dreaming up the technique helped someone sell a bunch of bow sights....