Speaking of stereo image and soundstage, and all that jazz, here's an interesting take by John Atkinson, editor Stereophile Magazine. The following paragraphs are excerpted from his article published in 1986.
"So there we have it: a perfect stereo image implies a perfect soundstage. All is rosy in the audiophile garden.
Hmm. A suspicious word, perfect. Where's the catch?
Well, we have only been discussing the interaction between the two loudspeakers and the listener. What about the amplitude-information only, two-channel recording? Where does that come from?
When it comes to recording music, there are two mutually incompatible philosophies. One is to capture as faithfully as possible the acoustic sound produced by a bunch of musicians, in effect treating a performance as an event to be preserved in a documentary manner. The second, which is far more widespread, is to treat the recording itself as the event, the performance, using live sounds purely as ingredients to be mixed and cooked. This, of course, is how all nonclassical recordings are made. The sound of an instrument or singer is picked up with one microphone, and the resultant mono signal, either immediately or at a later mixdown session, is assigned a lateral position in the stereo image with a panpot. As this is a device which by definition produces a ratio of amplitudes between the two channels, it would seem that every recording made this way is a true amplitude-stereo recording, capable of producing a well-defined stereo image.
Do such recordings have a soundstage associated with that image, however?
Sometimes.
When producing such a recording, the producer decides how much and what type of reverberation should be associated with each of the mono sound sources, and also decides where in space that reverberation should be positioned. There is no reason at all why the ambience surrounding, say, a centrally placed lead vocalist, should have any relationship with that around the drums. Or the guitar. Or the synthesizer. And if it doesn't, then the listener doesn't hear a soundstage. Rather, he hears a collage of individual musical events, bearing no spatial relationship to one another."