I'm not a scientist so I can't confirm that was the only factor, nor did I measure every corner of my pit at designated incrimates. I think it had to do more with when I would open the lid on a cold windy day the recovery time was less, similar to putting foiled, heated bricks in the pit. I had my temp set to 225, I wish I would have saved the graph. I could be wrong, like I said no official study, just my gut reaction.