Hi @tnoxel, thank you for reaching out to us and welcome to the Sonos Community. I appreciate you for providing us with a detailed concern and let me help you figure out what's happening.

Regarding your concern about the Sonos Arc placements. Arc has two up-firing speakers within it that sound best when positioned either on a tabletop, or wall-mounted below a TV. Also, Arc requires a minimum of 5.5 inches on the front and sides of it, with at least 2 inches between the backside of Arc and the TV when in a tabletop orientation. If wall-mounting, it is recommended to have a clearance of at least 5.5 inches between the TV and Arc. 

Let me also share these threads that may be helpful for you.

https://en.community.sonos.com/ask-a-question-228987/sonos-arc-placement-6846333
https://en.community.sonos.com/home-theater-228993/arc-position-using-a-wall-mount-room-impediments-6845117

We can also wait for suggestions and feedback from our Sonos community users for the setup that they may suggest or they have and about the Sanus BLF-328 wall setup in changing the height and the angle of the unit to the ideal sitting location. You may also contact our Sales Specialist for further assistance.

If you need help with any other information, please be sure to let us know.

Tnoxel, 

Did you go ahead with your plans for mounting? How did it work out? I have the same issue. One of the things that Sonos is not clear on their recommendations is whether the distance from the TV is from the front or the back. With my TV/mount combination sticking out 4”, my ARC will only extend 0.5” beyond that. I will mount it 5.5” from the bottom of the TV to the top of the ARC, but my question, like yours, is whether this recommendation assumes a flush mount TV.

Thanks!

Thank you for your reply to my message. Yes, I went ahead and I’m very pleased with the result.

I used two 1” solid oak shims in behind the Sonos bracket. I removed the magnet from the bracket first so that the Arc EQ wouldn’t be lessened. I drilled through the bracket into the oak shims with 4” screws that went directly into the wall studs. I installed the EchoGear in wall kit for the tv and soundbar - the kit soundbar wall insert is a perfect match for the Sonos Arc. All wires are totally hidden.

Hi Tnoxel & Sonos.

I too have a LG CX TV and Sonos Arc wall mounted with the Sonos Wall Mount. Sounds amazing!
But like you Tnoxel I have wondered if the LG CX is blocking some of the effects of the upward firing speakers?
Have attached photos and would like your (and everyone else for that matter) opinion:
Will I possibly get even better sound, if I use some spacers like you did? 
The LG CX is 8,5 cm (3,5 inches) from the wall. 
The top of the Sonos Arc is approx 12 cm (4,7 inches) from the bottom of the TV.
As I said, it already sounds great! And since the upfiring speakers are angled I THINK that the LG CX does not block the sound. But what do you guys think?
Hope to hear from you, as I am eager to explore the Arc and get the absolutely best possible Atmos sound :-)

All best from
Anders, Copenhagen, Denmark.
 

Hi Anders. Thank you for your message. I’m certainly no expert with this by any means. I would say though that if you’re happy with the sound you currently have that’s great. However, if you want to add a shim it isn’t going to harm the sound in my opinion. Your installation doesn’t appear to be as far out from the wall as mine, so you could consider using a thinner shim rather than a 1” like I did. I found the oak to be a very good choice to use for the shims from a vibration standpoint; MDF would be great to use too, since I believe that’s what stereo speakers are enclosed with. Whatever you decide I’m sure you’ll enjoy both your Arc and the CX for many years. 

Regards, Tim (Ontario, Canada)

Hi Tim. 
Thank you very much for this kind reply. I’ll try to experiment with some small spacers, just to see/hear if it makes a difference :-D