I would think it couldn't be much bigger...

Has everyone forgot the reason the peep sight works so well.
It has nothing to do with focus or visual sharpness on the aperture and everything to do with the eyes natural tendency to center something in a circle.

Stan I'm not sure why you're so dead set that this will not work when for years Winchesters lever actions had flip up peeps on the action tang two or three inches behind the hammer. No doubt who ever made this thought it worked.