It's a visual acuity issue. Learning to switch gears with your vision and accepting a different overall sight picture. At longer distances, we make the mistake of trying to acutely align/center the front sight with center of the target, but really loose point of reference of where "center" of the target is. This is where pulling back our vision slightly to accept a broader sight alignment by including the overall rear sight as a means of "cutting" the target in half. Also aligning the rear blade with the entire target now allows you to then focus centering the front sight into rear notch and firing the shot.
Does any of this make some sense, or does it sound like aimless ramble? LOL