The illusion of soundstage.

Wait, wait wait! :) HRTF is a real thing, that being said, I'm a huge believer in acoustic treatment and bass traps. If in doubt, call GIK Acoustics for a consultation.  

Not only do their panels work wonders on imaging and smooth great sound, their soffit traps have enabled my subwoofer and 2 way speakers to play to reference quality. I have so much lyrical, smooth and strong bass I can use music to treat kidney stones. :)  Soffit Traps FTW!! 

ahhhh! now i see. comb filtering dammit. that is great info guys! so its really all in my head , literally. makes sense. i knew there was more to it than simple external physics of sound waves, our ears are not the instruments we think they are. or at least not the simple conical sound gatherers with no other factors coming to bear.

Right, comb filtering is also created when sound reflects off a side wall and travels 2 different distances, that's why lack of acoustic treatment can ruin the spacial information. 

I know little-to-nothing about much of this discussion but I know what Wolf Garcia said is absolutely true.  IIn a stereo recording it all starts with the image created by the engineer's panning of the individual tracks/channels/mics. 
As to soundstage presentation in a mono format--I don't get the concept at all.

tostados, agreed, the engineer 'sets the stage'...virtually, but that's the modern recording studio for ya....not to mention the other 'enhancments' that can be dialed in.

I suspect that given current tech might allow a certain level of 'ambiance' in a mono recording that comes through with a high quality system, but I've never had the pleasure to hear such.  On the other hand, I'm not disposed to go looking, either...*G*