Most likely what you are encountering is the beveled edge of the meta peep. G5 bevels the inside edge so that if the peep isn't perfectly square, you can still see through it. You know what I'm talking about......it's those times when the string twists just ever so slightly. W/ that beveled edge, you can still see through it.

Second, I'm not a fan of the 1/4"....it's just too gosh darn big. Too much slop. The 3/16 is about perfect and honestly, there's very little difference in light between the two.