Getting the center speaker properly positioned is much more crucial with a speaker that has wide dispersion. Your problem is first reflections close to the speaker.
You center and mains have the same coaxial speaker, which is handling the speech discrimination band. You have already commented on the wide image. So that means a speaker with good wide dispersion, with the off axis mirroring the on axis. So now you have a set up where those early reflections, which your speaker will be awash with given the position, will give you poor dialog.
If you position the speaker correctly your problems will be over. You have a huge problem with that center being far too close to the floor, and other boundaries.
Lastly no speaker can ever by recessed at all. That is a rule you can not break.
This is the stand I ordered. It has a base large enough that I am hoping the Q650c will be able to fit right on top of it.
https://www.amazon.com/dp/B07M6114YM/ref=cm_sw_r_em_api_glt_fabc_XKVYVXP1T8B9R3Z4RDDX?_encoding=UTF8&psc=1
I do worry that as much as I like the KEFs wide sound stage, there is just something odd about them.
Last night, my wife was watching a show and the dialogue was just distorted and awful...it sounded like overemphasis of fabric rustling on people clothes. I questioned if the speaker itself was defective. So I set the AVR to stereo and I could pretty much hear the same through the mains. So my thinking is these just really reveal source flaws....but at this degree that might be an issue.
Secondly I through on a dialogue drive BluRay - Crazy Stupid Love. Dialogue was very echoey. Almost like I had set a music DSP mode like concert hall or something. So I again set it to stereo and it still had that echo quality. Which makes me wonder are these speakers really worth the hassle? Are they not really that great to begin with?
It also concerns me that without Audyssey running full correction, so much high detail is muted and they sound dull. I Like that room correction can help here, but it bothers me they need it to sound good. And I don't like very bright speakers either. Thats why I sent back the SVS primes within 2 days. They were just too harsh.
I say this because before I go tearing apart my setup and re-arranging things, I at least want to be doing it for a real upgrade. It's been the root question I've had: Are the KEF q series just not an upgrade over the older Polks I have?
I agree with you all that the placement of the center is not ideal, but for 14 years I had my CS400i that way and it sounded very good. I never had issues with dialogue clarity, balance, or odd artifacts like I am getting now. Thats why I started testing in stereo, to remove the center from the equation and just see what the mains sounded like and I'm not sure about them.