Gil,
When I had my shooting glasses made, the frame fitter (not the Dr), was a shooter. He not only understood that the optical centers had to be spaced per your eye spacing, but also that you don't look straight ahead through glasses when mounted shooting. He had me hold my head and hands as if shooting, then literally used a felt tip pen to mark the lenses for pupil centers where I was viewing through them. For a right hander, it is up and left and opposite for a left handed shooter. This reduces the distortion when in the shooting position.
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