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
"Then one "BIG" step further is to remove the back wall from in between the speakers like I did, leaving a little 1-2mt behind each speaker for bass loading"

Awesome George!
Thank you all for filling in a lot of holes in my understanding. I can remember my first experience of depth and soundstage size. It was in a small hotel room at a NY show years ago. The walls disappeared and there was a live orchestra stretching about 40 or 50 feet behind the speakers. Happened to be Swans speakers and Boulder electronics. I know that images can be behind or in front of the speakers, but didn’t have quite as clear a technical understanding of what made it happen.
"Then one "BIG" step further is to remove the back wall from in between the speakers like I did, leaving a little 1-2mt behind each speaker for bass loading" Awesome George!
It gave me double the depth and imaging that I had before with the wall in place.
Here is a rough drawing of it. https://ibb.co/9g5VW5W (when it opens click it again to enlarge it) , many in Australia have copied it after they’ve heard/seen what kind of image and depth it presents.

The speakers are ML Monolith III’s with the much better Neolith ESL panels, 12" bass drivers are much better than the stock one

And later if you need to sell the house, you just put in 2 x double fold away doors that fold back against each of the 2 short walls.

If you have a look my editor/reviewer friend of Soundstage he did similar with his after hearing mine with his Alexia’s, installing a big bay window between the speakers to give more distance, (the equipment rack is just in between for picture purposes and lives on the side out of site).
https://forum.audiogon.com/discussions/wilson-alexia-2-3

Cheers George

Looking at that picture in Soundstage the speakers are too close to the back wall or window as it may be. That's a very reflective surface to have a speaker in front of.

This seems to be equivalent to moving the speakers farther out into the room. This is usually enhanced with a diffuser panel between the speakers on the front wall.