For physical acoustics:
Any presence of a phantom speaker phantom Speaker a +speaker A and speaker B + phantom speaker b is the result of distortion caused by "speaker boundary interference effect" as well explained by my first acoustician video...
For psycho-acoustics:
We have 2 ears : then the speaker A will create by time delay for each ear a phantom speaker image a and the same for speaker B and his image b for the other ear...
Then the phantom image of speakers is not only the result of acoustical physical conditions but result in a stereo system by the way each ears will perceive each speakers with a time delay...
These facts illustrate how complex is small room acoustics and i used these facts with great result creating an holographical surround space with my stereo system...
In a word distortion is not a simple negative physical fact resulting from boundary interference effect but result also of our body organization (2 Ears) perceiving unnaturally the same sound from 2 sources (stereo system) ...
We must not simply eliminate distortion then , we must learn how to control it in our system/room....
It is not enough to understand physical acoustics, we must understand basic psycho-acoustics and learn how to use it...
This is why the balance ratio between LEV and ASW, between listener envelopment parameters and source width parameters ask for more knowledge (reflections controls and pressure zones distribution controls) than just basic physical acoustics about speakers placement as illustrated by my first acoustician video...