I am NOT aiming at the center, with a six o'clock hold, my point of aim is at the BOTTOM of a circle 6" in diameter. My bullet hits dead center (Well, more or less) of that circle, which is 3" above my line of sight.
In fact, I bought some Shoot-N-See targets lately that were 2" in diamerter. In order to hit these, I had to stick a 1" dot below my target as an aiming point, as without these, my shots were over the target.
I say again, and still say, my gun is sighted in for the distance the trajectory crosses my line of sight on the descending leg of the trajectory.