How to think about room correction settings like frequency range and gain?

[dominikz]

I really don't know what causes it but without the sub tuning with non-boost is impossible again. Below is a measurement with a slightly lower frequency on the sub.

IMHO this is very good already - I'd keep the sub as is and wouldn't touch it anymore for now.

The dip around 100Hz is IMO most likely caused by SBIR from the glass sliding door.
My suggestion would be to push the speakers back, closer to the glass. That should push the dip a bit higher in frequency, and might make it less deep.
EDIT: By the way, how far exactly is each speaker from its adjoining side wall at the moment?

Then re-run RoomFit, but adjust RoomFit correction frequency range to 20Hz-200Hz.

 

[Aziraphale]

The dip near 50Hz looks better. Have you tried playing with the phase control on the sub?

Not yet, it's on 0. I don't really know what that does, to be honest.

@dominikz Then I'll keep on the last sub frequency for the time being. At the moment the speakers are both 1.30m from the side walls and 23cm from the closest glass. How close to the glass would you put them?

Only thing is that the window frame is right behind the middle of the right speaker and completely to the left of the left speaker, which makes them slightly less symmetrical from that point of view.