Rather than wall mounting the speakers, you might consider using a pair of narrow console tables that are about the same height and width as the back of your couch. See the example from my post on this thread:

Sadly that wouldn’t be an option for me as I don’t have enough space in the living room to move the couch closer forward.

I wonder whether in-ceiling speakers may be a better option?

Unfortunately, few rooms are optimal for speaker placement. My living room is no exception, I have a fairly large U-shaped sofa in a corner, my TV is placed sideways from the sofa on a wall bracket so I have to pull it out from the wall and angle it when I watch TV/movies. I had to place my Era 300 on 2 different walls where the side of the speakers hits my ears when I watch TV/movies. 

It's far from optimal, but it works pretty well and I get a good sound image.

The Era 300 should be placed at ear height when you sit down. In your case, I would see if they could be mounted on stands but otherwise on the wall as you mention. The wall brackets can be angled up/down and to the sides, but they are not easy to angle so that they have the same angle as they do not go into clear notches. So it was quite a project to get them 100% the same angle.

Once mounted, run a quick trueplay and adjust the volume from your Era 300, that way you get the best possible sound experience.