Here is a link to a rather bizarre video by Tony Northrup who has done a lot of videos and seems to be offering training: https://www.youtube.com/watch?v=DtDotqLx6nA
Am I glad you used the word bizarre to describe that video…. I watched it once, twice, then three times and kept going “Huh?!?” I finally went back to your post and saw
The thing is, it’s not how much light the whole sensor gathers, it’s the amount of light a single photosite collects that determines the signal to noise ratio for that photosite, and for a scene reflecting x lumens toward the lens, the same lens, same focal length, same aperture, etc., the amount of light received at some photosite near the middle of the sensor will be the same as for the photosite in the corresponding position on the other sensor.
and I was saying “yes, yes, yes!!”
I think to get exact DoF measurements, you’d need a calibrated optical bench with micrometer calipers, although your experiment seems accurate enough for me. At the end of the day, the numbers mean very little if the photographer doesn’t understand the concept needed to produce consistent results.