No one doubts that the AFOV's are as reported. They simply don't matter. All that matters is the RFOV and/or the field stop diameter. The AFOV will not tell you how much sky you will see. The RFOV and the field stop will tell you how much sky you will see. And the RFOV (or the field stop) will tell you without measurements of any nature, provided that the manufacturers get on the stick and accurately report these values.

I would most certainly like to know more about your method though!!!