Les:
Weren't you on here years ago asking about benchrest on Hawaii?
The square is to facilitate sighting in extreme mirage.
Scope picture depends on whether you are shooting group or score BR. Score shooters would like their point of impact to be the same as their point of aim and their scope picture would have the crosshairs exactly on the dot (or X ) in the center of the bull. This is also why score shooters want a scope with 1/8 minute clicks. Group shooters typically prefer to have their group outside of the heavier "ink" of the bull as it is thought they one receives a less favorable measurement when the heavy 10 line is at the edge of a group. Therefore group shooters have a myriad of scope pictures. Some aim at the 3, 6, or 9 o'clock edge of the circle. Some will set the bull in the upper left, upper right, lower left, or lower right quadrant of the scope's crosshairs so that the group is outside the bull but close to point of aim. I hope I didn't muddy your scope picture with that explanation.
