Lots of sound advice (pun intended) above.

I'd just add that as well as speaker position, the listening position is just as important.

Often you have less flexibility with that but, in my experience, the distance from back wall to listening position is just as important as speaker placement.

Same is true of side walls but often the listening position is already mid-room laterally.

With glass (windows/doors) behind for the OP that will be more so as it is hard to tame the reflections off the boundary behind the listener.

I've tackled this with great results putting acoustics traps behind the listener. But I know that is super hard with glass (you have to innovate).

It's worth testing this by simply moving forward and backward from the listening spot as the music is playing. Note how the balance of the sound changes as you move into peaks and nulls created by the reflections of the back wall.

Somewhere will be a sweetspot for a given speaker placement. As you tweak the speaker placement the sweetspot moves.

It's tricky but trial and error wins.

HTTH

Rgds,
Nick