I did not touch my setup and MiniDSP settings since November 2020 since I was happy with exercise I did and posted the result at
https://www.hifivision.com/threads/venturing-in-rew-umik-1.81299/post-914275
Today just to experiment, I followed
as you did.
One of the parts which was different in this Video and I have never done earlier during MiniDSP setup earlier was to set the Level of Sub on AVR as "0".
Today after I did it and I approached level matching ... I had to really cut down on the gain on both Subs (to bring the level to 75 while Master Volume on AVR was -18db. This was followed by the Gain on MiniDSP plugin (to the sub placed near me).
This messed up all my subsequent measurements. Thankfully I was experimenting in Config 2 tab and I immediately shifted back settings to original Config 1 which I achieved in November.