Wow, this was a really interesting discussion. Thanks to all for sharing your thoughts and for making BIR look more like a science!
I would like to throw another thought into the mixture, but I'll make it in the form of a question. At what temperature do BIRs keep their base throughout the day and how frequently do they re-heat it?
I've seen videos of stockpots of base on top of BIRs and I've never noticed them having any flame going underneath, which sort of suggests they probably only turn the heat up every now and then - if at all. Thoughts?