If you have a certain rear sight location in mind, make a 'try sight' from electric tape, and put it on the barrel, throw the gun up to shoulder, see what the sight picture looks like. If you can't get a good sight picture, widen the notch. If you still can't get a good sight picture, make a new tape sight, and move the rear sight closer to the muzzle, and go through the process of widening the notch until you get a good sight picture.
Tom