Image depth


Can anyone offer a technical explanation of how a stereo system recreates image depth? Why are some center images behind the speakers, and others in front of the speakers, for example.
Should there be any depth to a mono recording, or should the image be directly in line with the speakers?
cakids
Furthermore, it seems to me that a few microphones, no matter where they are positioned during recording, cannot possibly duplicate a music waveform’s ampliture and phase exactly as it would occur at a live listener’s ears. So how can an accurate soundstage be created?
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Do an internet search using the phrase "stereo recording techniques".  There are a vast number of articles describing different microphone placement and their impact on stereo sound reproduction.