When I competed it was easy....you installed a front aperture in your front sight that was just bigger than the target bull so your eye naturally centered the bull in the circle...but that was with a known sized bull at a fixed distance. No such luxuries in hunting!

Not sure what you call it, but with a leaf and post/globe I set the sights so that I level the top of the front sight with the rear leaf, and the bullet will impact right at the top edge of the front sight. That way the target size has nothing to do with my sight picture, I am aiming for a discrete point that sits right at the top of the front sight.

I never did understand the ones where they wanted you sitting the bull on top of the front sight like a ball on a post. Bull size and target distance will both change the point of impact significantly.

As for distance, typically I only shoot irons if I plan on the shot distance being 100 yds or less. I will zero a bit high at 50 yards, then fine-tune so I'm on at 100 yds.