This is exactly what I was expecting, thanks for going thru all the work to show this. Getting the antenna mounted externally on the vehicle should fix the SXM reception.
You can use the FAKRA Z style cables which are universal fit rather than having to hack the other ones…
https://www.amazon.com/dp/B07P2VBYWZ?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1