My trouble, and I suspect a lot of you grey beards out there, is that a flat topped rear sight becomes indistinct for my vision. I cannot tell when the front sight is level with the rear, as the rear has an indistinct top. So I get vertical stringing. A sight such as that great diopter sight of Dan's will clarify the top of the rear sight and give a perfectly distinct sight picture.
For a traditional longrifle, such a sight will not likely be allowed in most competitions. So I have come to rely on the English "B" sight and a bead front. The "B" sight in my case, has angular rather than curved lobes, that end in a very shallow "V" in the centre, so that all I have to do is roll the bead of the front sight down into the bottom of the "V", and cover the bull. The bead front sight is placed directly over the bullseye, and the ball goes through the centre of the target. In other words, cover the target's centre with the bead, in the bottom of the rear sight's big fat "V", and touch her off. This sight also is aguably the best and fastest hunting sight, especially in failing light .