Welcome fellow Motif owner! My mains are Vistas. My living room is the mirror image of yours!
I originally had my center where yours is, then moved it to the top of the tv stand, and now it works much better above the tv. I tried all sorts of settings on my pre-pro as well as using the on-wall/off-wall switch on the Motif but it always sounded just a bit "boxy" until it was placed above the tv.
My mains have moved many times trying to chase better imaging and minimizing bass bloat in certain seating locations. Currently my mains are 6' from the front wall and 40" from the side walls to the center of the curvilinear front of the electrostatic panel. If my room were flipped to match yours, the width is 13' from the side wall to the left of your tv to the far right side wall on other side of the hallway. My ceiling is vaulted so to the left of your tv it's 8' high and on the far right it's 10-1/2' high. Using some of the speaker placement formulas you come up with where my speakers ended up, (knowing the formula would've saved me some time), I used trial and error to get to where I am. The bass is now the smoothest it's ever been in the sweet spot as well as across the seating area, which is a straight sofa and a chair next to sofa. I measured the bass spf for each frequency manually just watching for peaks and nulls.
When the mains were close to the front wall I experienced mid and high confusion and not very good image. A couple feet into room and things improved. At about 3' the mids, highs, and image started coming into focus, but bass was still an issue. At 5', things really snapped into focus and the bass was only a problem on one side of the sweet spot, it was bloated and boomy. That one extra foot made a pretty big difference for expanding the sweet spot!
For the last week I've been moving diy absorption panels all over the place. I won't really have time till the weekend to play some more, but I'll probably end up with just a few first reflection and some bass trapps.
I've found that at lower volumes a lot of amps will work just fine, but when I moved into this house and was able to crank the volume, I was in the hunt for a really good amp and preamp. I am very happy with what I now have.
I hope some of this info helps.