Your eye will automaticlly put the top of the post in the center of the rear opening. How to hold the top of the post ( and adjust rear accordingly ) is up to you, and your useage.
If bullseye shooting, at a constant size bull, I think most shooters will adjust the rear sight so the top of the front post is right at the bottom of the bull ( lollipop ).That way a hold can be consistant, from shot to shot.
For hunting, with a post front, I think most folks will adjust sight so the bullet lands right on top of the post at the sight-in range. With a bead front sight, it would either be the same, or else sight-in so the bullet strikes the center of the bead, i.e., the bead covers the sight ( obviously best for close range ).
Mark