Jeff, I applaud your efforts. If you have any inclination to test this further (and I think you should), I'd really like to see a traditional fire on the side with a fairly active flame top licking flame for the test. It would also be nice if you could do the test near the end of the bake, just to make sure the super-heating of the center of the hearth during the initial fire isn't messing with the numbers. Lastly, could you take measurements of both the tops of the bricks and the fire facing sides?
Now that I've hopefully somewhat explained my thought process I better get off the computer and on the phone to the Journal of Pizza and tell them to stop the presses pending further peer review, lol.
You joke, but the real world ramifications of this information could be substantial. If conduction is the major player, then all these countless high dome oven owners could, in theory, place some sort of insulating layer (perlcrete) under their fires, go with larger, more aggressive fires and possibly end up with a more Neapolitan-ish top bottom heat ratio. This would most likely burn through a lot more wood, but... for a more Neapolitan-ish thermodynamic, I think it's a price many would be willing to pay.