If you find out that you may be half peeping, it may be beneficial to size your peep so that you can center the whole sight housing.

I had this same issue a couple of weeks ago at an indoor marked yardage tournament. I could not center the housing because of the lighting. It messed with me all day, I painted the lens ring and had no problems the following weekend down in Nevada with centering as I painted the ring. Just a little can mean being a couple of yards off.

I have experimented with half peeping on pins to get my in between yardages and know the effect it can have when your are not centered.....

Try centering the housing on every shot and see what happens......