And another idea regarding the h-number.

To me it could be defined like this:
#1 Take a picture of a gray card, properly focused, with the Imagon fitted with the special iris. Focus with the outer array of perforations closed, then re-open. Measure the illumination in the image plane.
#2 Substitute to the special iris a simple circular hole centered on the optical axis, located in front of the glass at the same place, do not re-focus in order to keep exactly the same distance between the glass and the image.

When both experiments yield the same illumination, the h-number in #1 experiment is equal to the regular f-number in #2.