Sound stage

"How do you know when its right?"

To start, get something like the XLO Reference Recordings CD, which has tracks that will walk you through where you should be hearing things. If you hear what the narrator tells you should be hearing, then you're on the right track.

back when stereo first hit, soundstage and imaging was a big selling point. You can find old lp releases on Mercury Living Presence and others that go into great detail in teh cover notes how the recordings were made and what was located where during the recording session.

Soon after the novelty wore off and most people did not pay attention to such details. Except us audiophiles, of course.

Yea especially in early Beatles stereo pressings L:)

Staging is a function of both recording and playback equipment. I'd also agree with previous posts that there's no "perfect" paradigm that you're seeking for all recordings. Highly processed or manipulated recordings can even cause you to sense images that seem to be coming from behind your head (check out many of the Qsound recordings for this effect).

Heavy pan potting (Theme from Shaft, among many others) can create shifting instrument locations that are part of the intended artistic effect. You can seek out minimally miked records for purist stereo effects, but that approach is too limiting (in terms of music that I enjoy) for me.

I'm also in the camp of using recordings (or test discs) that are known for center fill, width, depth, phase, etc. and set the speakers up so they're optimized as best as possible across all parameters and then just leave them there -- unless something else changes of course. Recordings vary across and even within genres (and even sometimes individual recordings!) so greatly -- for better or worse -- that trying to optimize for each recording just seems like a fool's errand with no end. I never move my speakers, and if there's an occasional recording where something seems off I'll try to correct it with the balance control. If that doesn't work I either just deal with it if it's a recording I still really want to listen to or I'll listen to it in my car or through another less critical system where the flaws not as apparent. Or it goes on the shelf to collect dust or gets sold.