Hopefully this was a helpful write-up. I think your measurements are really cool, so I just wanted to share some of my experience from the pro-audio world. AudioScienceReview has a bunch of great resources as well, as does the AES library.
To create a spatially averaged sweep, you must perform at least 6 (preferably more) measurements in a sloping rectangular pattern around the driver position. In REW, you then cross-correlate align the impulse responses, and then perform "RMS + Phase" average of the responses. What you're doing...
Super cool to see others taking in-situ measurements of their audio systems. I actually made an account just to reply to this thread with some tips regarding your measurement methodology. I came across these posts as I'm considering buying a pre-owned Rivian, and audio quality is very important...