Its my understanding of batteries in general that they are rather sensitive to temperature as far as charging rate, capacity, and power delivery as well. We went over that in Physics class. Furthermore, the HCH is even MORE sensitive to battery temp and SoC in order to maximize battery life. So even though the battery may not seem like it changes much over a couple of minutes, it does, and the regen will respond accordingly.

The fluctuation of the IFG IS a calibration. Its in the manual somewhere. It just happens kinda often, which I find weird. Makes me think its a bug sometimes, but I'm sure its just that: a calibration.