However, the single most important factor in audio stereo imaging, is increasing direct radiation and decreasing reflected radiation,
Mostly. Diffraction in between and on the sides can sometimes enhance the experience with more ambiance and more volume in the mid to high frequencies, enhancing the realism.
by moving the speakers away from the back wall, and away from the side walls.
That's an important first step, but it is by no means the only one. Room treatment in all 3 dimensions matter.
It is also true that different speakers work differently in their interaction and reflections, so there's no one ideal treated room. Line sources and horns for instance may work better in bare rooms.