I had 12 inches of space behind my 6ks and and about 18 inches to the side walls. Sounded great but wanted to tame some bass, so moved them into the room by about 6 inches in both directions.
Made quite a difference. So thought can this keep getting better?
Settled on speaker fronts being just over a meter out into the room from front and side walls.
What a difference. Bass tightened up. No boominess. Mids opened up massively. Airy. Far more detailed.
Get your speakers as far out into the room as you possibly, comfortably can. You won't regret it

Good luck

Nick

861v8+ID41, HD621, DSP6000, DSP5500HC, DSP6000, 2x DSW's, Roon, AudioQuest Niagara 5000, IsoTek Titan, Nova, Vision, Mira.