I would not be able to shoot Fowl's sight. It's too narrow for my aging eyes to see. When I was younger than 40 - yes- it would work, but definitely not now.
Widening the rear notch, as Taylor, Len and Neil have done on their longrifles looks good to my eyes, but so far, my guns have a narrower V notche which also seem to work. (those without wide shallw "V"'s that is.)