When people say "Eye box" what are they referring to? That might refer to my problem of inconsistent cheek position. I have a hard time getting the same sight picture and my groups suffer because of it.
They're referring to the area in which you can place your eye and still get a good sight picture - i.e. not seeing a shadow on any edge of the scope. Your problem could also be related to parallax which results in the crosshairs moving when your head changes position. Scopes without a side-focus usually have a parallax adjustment at the eyepiece. A quick way to check for parallax is just to move your head a little bit while focusing on the crosshairs - if the crosshairs move to point to another spot, you have parallax issues.
HTH,
GsT