So your large oven has a capacity greater than 14X that of your smaller roaster oven, and consumes under twice the kWh, huh. Did you run these tests with the ovens empty or at normal baking loads?
Can you describe how you made these measurements?
Kill-a-Watt type device? Clamp-on ammeter? ??
And what other items may have been consuming electricity during the 10-hour period the large oven was on?
All things considered, it makes the large oven look like a real winner for efficiency. I suppose the next step in the progression would be to bake an identical something or other in each of the ovens to see how much electricity each consumes during active use.
Interesting investigation, Chris.