I have now learned to use my hindsight before placing too much emphasis on the foresight.
There is also the style of blade and notch, which affects clarity, hence spacing. I don't want to get too far off topic, as I am wont, but the best kind of sight is not necessarily what was used in the 18th century.
For me, a square wide front blade is the easiest and sharpest. Make a rear sight notch wide enough to give a crisp image of the front sight. You can make a mock rear sight with electrical tape, keep cutting the notch wider until the front sight is clear.
Many old rifles use the barleycorn sight, which I can no longer see. Or I see two of them.