gdhal,
Those observations are slightly different.
It is true when I describe the projection that results in a full stage shift
caused by the slight offset in distance between the speakers and your ears. If
you were sitting in the hall for real and your turned your head slightly to the
right (making your left ear closer to the stage) would it not appear that your
perception of the stage has moved slightly to the left?
Regarding the sweet spot. Here is where I may get into trouble.
A portion of the "sweet spot" is directly caused by distortion. Surprise!
Both stereo channels have the same circuit. Having the same circuit means
they behave identically. Whatever distortion is present in one will be
present in the other.
When full spectrum music is played, the distortion product in both channels
will be the same and it (the distortion) will manifest itself as an [additional]
sound object all by itself. To the observer it sounds like a monophonic
"entity". In order to experience the "spot" you can move
your head from side to side while looking straight ahead. You will sense a moment
when it seems like you hit a focal point of significance. Depending on how much
of the music is close to common (centered or vocal mic mixed in as mono) you
will have a distortion object added to your presentation. That object is dead
center (assuming close matching of circuit components). If your speakers are at
slightly different distances it will not be dead center.
This can be confused with an actual sweet spot created by the polar dispersion pattern of your speakers and how the venue was captured.
Because of the nature of H-CAT - after the electronics is burned in – the final remnants of the common distortion product disappear and you will be able to perceive a wide open sound stage that can be “viewed” from many listening positions. If this were not true then only the people in the hall who are seated dead center would have enjoyed the performance.
Roger