Don: If you try looking at both a narrow and a wide front sight, you will find that the wide front side is easier to see in different lighting conditions. Anything is easy to see on a bright sunny day, no matter how small or narrow. With the wider sight, as with all sights, you don't look at the whole sight, but at an imaginary line down the middle of the sight. Take a handgun out and shoot a pop cans, not at a few feet, but at 100 yds. You will find that the can appears to be much smaller than the width of even a handgun front sight. The way to hit the can shooting that short barreled handgun is to imagine a thin line down the middle of the front sight, and align that line under the can. The same thing is done when shooting rifles, only the wider front sights are much easier to see in bad lighting, and with shotguns when shooting round ball or slugs. Open the rear sight so that there is as much daylight on both sides of the front sight as it appears in that rear sight notch , as the front site appears to be wide in the rear notch. In effect, you want your notch to be " three front sight widths " wide, and how wide the front sight depends on the actual width of the front sight, And the distance between the rear sight and the front sight. The longer the distance between the two sights, the smaller that wide front sight will be.
Some shooters have found success in eliminating windage problems on rifle and slug gun sights, by etching, or scratchin, or painting a thin line in the center of the notch on the bottom side facing the shooter. This gives the shooter a reference point to align the center of that front sight. I don't find any benefit to making a line on the center of the front sight, simply because sun light shines off such a line, etched, cut, or painted, differently when the light strikes it at different angles as the sun moves through the sky. I have tried front sights with centerlines, and elevation bars, and none have produced consistent results. The alignment line on the back of the rear sight notch is a small help. Having shot peep sights quite a bit, I now simply look over and through the rear sight, and not at any part of it, concentrating on the front sight and its position in relation to the target.