ptss
Regarding the wall behind the speakers. Regardless of the type of speakers the wall is a reflective surface. There will be a time delay between sound from the speakers and that from the wall. This is Distortion.It’s really only distortion if the speaker system was designed to play in an anechoic chamber.
If you want refined,delicate,nuanced sound,at all volumes, this distortion Must be avoided.How would you do that, short of an anechoic chamber? Or using headphones?
Even at 40 inches, you’re still getting reflections off that back wall. I think the more important question is: How did the speaker designer intend for the speakers to be placed? Typically, dipoles are intended to be used away from the back wall. But many other speakers are designed for closer placement to the wall.
... keep speakers away from that wall. I like a minimum of 40 inches