I had looked at that and maybe I just dont understand their terminology...
If by Thin opening they mean from the top of the bottom thick picket to the bottom of the top picket the I can say that is right at a 100 yds min zoom.
If by heavy section they mean from the top of the cross hairs to the center of the cross hairs then I could agree..
If by thin section they mean.... no idea..
In the attachment is a pic of what I am trying to get the distance from:
figure a - from center of cross hairs to tip of top (or bottom for that matter) thick picket.
figure b - cross hair tip to tip.
figure c - from bottom of cross hair to tip of bottom thick picket (the gap).
I could see how the heavy section they say is 2.1 could be the thick picket thickness, the thin section the thin cross hair thickness and thin opening maybe the size between the thick pickets...
Hopefully I will get my email answered before the season ends. I have some shots pushing 400 and I want to be able to compensate on the 100 and 200 yds mark as well.