Ok, I feel like this is an extension of another post I just made in another discussion about imaging.
I used to sell audio, I have some experience setting up different kinds of speakers. They vary dramatically in their optimal placement from walls. So no one rule works, despite acoustic treatments or DSPing being helpful. If you have a port in the back of your speaker, it behaves differently than a sealed acoustic suspension, which behaves differently than dipoles. Some are made to be against walls or made to be placed in corners (I sold Klipsch speakers).
I used to sell audio, I have some experience setting up different kinds of speakers. They vary dramatically in their optimal placement from walls. So no one rule works, despite acoustic treatments or DSPing being helpful. If you have a port in the back of your speaker, it behaves differently than a sealed acoustic suspension, which behaves differently than dipoles. Some are made to be against walls or made to be placed in corners (I sold Klipsch speakers).