I can casually talk without having to raise my voice at all to talk to the clients while listening at 10-12 ft in front of the speakers.
At 12 feet back you lose 12 db. Asuuming you want at least 10 db of headroom then you are going to need a decent speaker, preferably with a pro woofer that does not badly compress when driven hard.
If you are judging rock at normal conversation level with your clients then this might be a bit too low a level for bass checks - you'll end up with overly bass heavy mixes unless you can adjust for it in your mind.
You want a speaker with a wide sweetspot and NOT a narrow dispersion monitor like a Dynaudio nearfield.
ATC will do the trick for you - will give a very large sweetspot for you and your clients. A larger Dynaudio or Merlin would work also but you said you don't want a floorstander - so I would not go that way....besides you have three near-fields already.
I'd also seriously consider adding a good tight subwoofer like JL F113 and have everything in room calibrated with a measurement microphone - see my virtual system for calibration plots.