[Mag]

 Just my opinion here. I've been watching Audio Shows on Youtube, Munich, Warsaw, New York, Toronto, etc.. I see a lot of set ups, Many due to room size have speakers placed relatively close together perhaps at best 5 feet apart.
 Now the purpose of Stereo is to create a phantom image. In these type of set ups the phantom image is at best narrow or weak which usually happens behind and between the speakers. If you are not hearing a phantom image then you are most likely hearing Folded down Mono. Nothing wrong with that, just that it is not Stereo.
  If you do have proper separation of your speakers you still maybe listening to Folded mono. It maybe difficult to discern the difference between stereo and mono but if you don't have a phantom image you are not listening in stereo.

[Letitroll98]

And those placed directly against the wall.  I see this more than closely spaced speakers.  Even my HT speakers are out from the walls.  You still get a stereo image, but no depth of image, which is a key component of stereo imaging.  That being said, all this can only apply to audiophiles.  One of my sons cares nothing for audio beyond how does it sound playing games with his buds.  The other son has an interest in audio, I refurbished a nice turntable for him, but the speakers I gave him are next to the ceiling on top of the entertainment furniture because "that's where they fit".

[Mag]

Typically you'll see the conventional stereo setup that creates the phantom stereo image. This setup IMO is somewhat speaker dependent, the more accurate the speaker the better the image. I however had smallish tower speakers that could create the phantom image. So IMO it has more to do with how the speaker sound interacts with the room boundaries and not necessarily in a conventional set up. Finding this spot may not be a practical place depending on your room.
  I use an unconventional set up using reflected sound in a far from ideal room. Producing a 15' x 8' phantom stereo image that is strong and solid sounding,  however depth of field is lacking because speakers are close to the front wall, but I can live with that.