I have practically every type of 'notch' imaginable on my rifles and pistols, and they all work just fine. What you need is a sight that you can tell when the front sight is LEVEL with the top of the rear one. A sight notch that is too small will fuzz this out and you will make elevation errors when shooting. This too has much to do with your vision. For folks with bad eyes, I have often used an absolutely flat topped rear sight with a vertical gold band down the middle and no notch at all. This rear sight slopes forward, rather than rearward, to catch light and illuminate the gold band. The front matching sight in that case, is a post with a 45 degree filed to the tip which catches light, and to the eye, looks like a round bead. Now it is simply a matter of putting the 'pumpkin on the post, ie: the bead on the top of the gold band. I encourage shooters to hold the bead where they want the ball to go..centre shot, no six o'clock hold stuff. How do you hold six o'clock on a tack or horizontal string?