I was surprised that the battery was nearly 90F where the BMS resides.
Yup. That is always the case when charging. Module 6 is the hottest, followed by module 5. They are up under the seat with the BMS, and the fuse. However, I don't think it has anything to do with the smoke usually coming from under the seat. That is the only opening in the battery cover into the car. It is at the highest point, and certainly the plastic fuse holder melts pretty quickly. If you were going to make a chimney into the cabin, this is how you would design it.