The configuration you linked is an f/11 instead of f/20, and your clear aperture is 72 vs 76 mm.
Yes, both my meniscus and my friend's has a clear aperture of 72mm. I just measured mine again and the CA is 72mm and the physical OD is 76mm. We both tried to get the design to work with the radius we measured. We both got similar results but like I said I couldn't use my spherometer to get exact values but with what we measured we found F/20 wouldn't work.
There are a number of small Maks spotting scopes that look to possibly be were these optics are being used and they are in the F/10 to f/15 range but we couldn't find a F/20 example.
As I said before we got these sets back in the Spring while SS stated they were F/20 as well, ours might be different then what is being offered now.
Here is a picture of my friend Matt Considine's setup to test the optics.