Looks good.

I am surprised you went with a loaf pan. An esbit stove or cup wouldn't be able to hold as many candles but would be lighter and more compact. It would be interesting if you could weigh the candles before and after, so you could get an estimate of how much heat you are releasing.

I think you have the theory down pretty well. To add to what you said: The candle produces mostly radiant heat which is being emitted around the tent. It will heat up surfaces in proportion to how much area is exposed to the candle flame. That means some would be absorbed by the sleeping bag but quite a bit would be absorbed by the walls of the tent. Since the tent walls are so thin, much of that heat will be lost to the outside. By using the shields and rocks, you are absorbing most of the radiant heat and storing it at a lower temperature. The lower temperature means considerably less will be transmitted radiantly. Since the energy is not being radiated away it will warm the air around it and more will be contained within the tent.