Couldn't you do it at 0" also (Which is as you stated less than a foot.)
The pinhole aids focusing down to a smaller distance. (May aslo help with the parralax problem i.e. "Head bob". Aim at the cross hair (what you defined as Point of aim) and see how far it drops.
(Edit, added "Head bob" and "point of aim" in explanation and corrected a typo)
Joe <><
href="
http://www.hamcontact.com/airgun/HoseAssembly/