Plink: I used to think it was best to leave the notch alone, until clouds rolled in one day and I was having a harder time seeing my front sight in the " Precise " little notch. I finally got mad- mostly at my failing eyesight-- and opened the notch up. I find I can align the sight just as accurately with the wider notch.
I have since opened the notches on other sights, and done much trial and error, and find target accuracy is not hurt with the wider notch. I thought it may be solely MY eyes, but I asked some other shooters to try my guns, and even the best of them, with great eyesight, remarked how much nicer it was to see more " daylight " on the sides of the front sight, with my wider notch, than they experienced with the narrow notch. Some of them wanted to open their own sights, but were afraid to trust their own hands to do the file work necessary, fearing they would screw it up.
For quick sight acquisition in iffy lighting conditions, I paint, or file a verticle line in the center of the back of the rear sight, to use to align the rear sight with the front sight blade. I long ago learned how to concentrate on an imaginary line down the middle of my front sight blade, as a revolver shooter, and I use the same thing with rifles, to avoid windage errors.
When I was cutting playing cards on edge, or splitting my ball on the edge of an axe to break two targets with one ball, in exhibitions, windage became far more a concern than elevation issues. The wider notch, and that center line helped me do the " tricks " and please the crowds.
I laughed the other day seeing a rerun on the History channel when they had Bill Oglesby do these shots, and described them as very difficult shots. If you are interested in doing this kind of trick shooting, read my article on Off-hand and Trick Shooting under Member Resources on the Index page, here. I give away the " secrets" to doing these "difficult" shots.