I'm sorry. I misread what you were asking.Thanks so much for your reply MagnumX, but I'm not sure I totally understand. I should also clarify that my 2 Atmos speakers are in ceiling speakers.
The angles are kind of far apart so normally I'd say no to putting 5.1 surrounds that far back, but I just listened to a Quad music album (Billy Joel's Streetlife Serenade) that makes me think it might work better than overhead speakers do at such distances. Namely, dumped to ISO (PS3 can extract them), the new version of KODI (V19 Matrix) with the new SACD plugin allows it to play back SACDs directly now and with a quad album, KODI can use either side surrounds (set to 5.1 output fixed config in KODI) or alternately the rear surrounds (set to 7.1 fixed output) for the surround speaker output from that album.
I tried it both ways and I was surprised to find I still had many sounds appearing off to my sides when using fronts + rears for quad output (side speakers were silent so images were phantoms between my rear speakers and mains even though the rears were about 12.5 feet behind me and the fronts are 7.5 feet in front of me). I get weak overhead imaging trying to phantom image that distance without Top Middle so I was surprised how sharp the side phantom imaging was with ear level speakers that far apart.
It's possible the human brain does better combining ear level sources than overhead ones at greater distances. In any case, that experience makes me think it's worth at least trying (i.e. I'd try it with cable across the floor even just to hear what it does before committing to a location either way unless You're stuck in terms of usable locations in the room. Speakers and rooms can vary a bit.
Quad was actually designed for equidistant speaker placement at the center of the square/rectangle so movies might not image as well further apart, but I'd be curious to know how well it works if you try it. I'd have to rewire to try it it out with movies that way here.