I would put the Era 300s on speaker stands and place them behind the sofa on either side and facing the front wall directly. You would have to move the sofa up a little and move the shelf to the center of the wall.

Unfortunately there’s not much space to move the sofa forward. It would make the room really cramped and as it also doubles up as guestbed I’d have to move it back whenever we have guests (as there wouldn’t be enough space to open it up otherwise), which would also mean moving the speakers.

Can you wall mount the speakers?

Yes, that was my original idea but I don’t know if it would work.

Maybe downsize to the 100s for the smaller size? Stands or wall mounts would work.

So how would I place them? Mainly, how high should they be placed in this case? Can they be placed near the ceiling? How much does it affect that the other wall is farther away by quite some distance (percentage-wise)? Left rear speaker would be quite close to the side wall.

Of course the big loss would be Atmos if I downgraded.

Hm, found the user guide for Era 300s, which state this:

• Era 300 should be placed indoors and have approximately two ft (.61 m) of overhead clearance for optimal sound quality. Placement in an enclosed space like a bookshelf is not recommended as this could impact dispersion and playback clarity.
• If you are mounting Era 300 within 2 ft (.61 m) of a ceiling, place it upside down for the best sound.
• When Era 300 is placed next to a wall or on a shelf, leave at least 1" (2.5 cm) clearance in back and 8” (20.32 cm) on each side of the speaker.
• When using Era 300 speakers as surrounds, leave at least 8" (20.32 cm) clearance around the sides of each speaker.

I could place them quite high, near the ceiling and turn them upside down. This way no-one would accidentally bump their heads into them when getting up. And I might be able to just about place them 2ft below the ceiling and not have this issue. I could leave that 8” to the side of the left speaker as well.

I’d give them a test-listen at ear level, then try other options to see which position sounds acceptable.

Had a convo with the SO and it sounds (pun intended) like 300s are a no-go to that space.

So how about 100s? Worth it? Would I get a much better surround sound experience with them? Someone already suggested these above and I guess I need to revisit this idea or forget about rear speakers altogether.

Ok, another possible solution could be to install speakers near the ceiling and turning them upside-down. Would they then still be installed pointing straight forward?

I feel your SO issues, my surrounds for my Arc are a set of Play 1s, sitting on top of a six foot tall, three foot wide bookcase stuck in the raer corner of the room with the Arc in the other.

I don’t do much Atmos so my Ones and Play 1s meet my surround needs quite well, 100s would be a nice step up. They are also much more forgiving in placement than the 300s since they don’t do Atmos.