I think we are now stuck in a dead end without measuring. I don't know how much it is worth to buy a USB measuring microphone? It would be much easier, we guess a lot like this. A simple program like HOLMImpulse and you know everything right away.
https://www.minidsp.com/products/acoustic-measurement/umik-1
https://www.daytonaudio.com/product/1116/umm-6-usb-measurement-microphone
https://www.minidsp.com/products/acoustic-measurement/umik-1
https://www.daytonaudio.com/product/1116/umm-6-usb-measurement-microphone