Imaging/Soundstaging - Does room size matter?

More info on room setup, speaker placement, etc...

The speakers are set up according to the Cardas Golden Triangle system. The room has been treated with foam and such, but it's not acoustically perfect.

Which wall are the speakers located on?

I had two systems in two different rooms. The system in the larger room, with the speakers out into the room and wide apart, has a wide and deep(!) stage. But the width of the stage stops at the speakers.
The smaller room only allowed for the speakers to be maybe two feet from the outside walls. The imaging in this case was realistically beyond the boundaries of the speakers, width and height too. Although overall the soundstage was smaller, the music did not appear to be coming from the drivers.
I think maybe the "acoustic support" of the side walls can actually improved imaging.
But I could be wrong! They were different systems. I would be interested in what others have to say.

I am inclined to think that off-center images being localized at the speakers may well be a loudspeaker issue rather than a room one. Maybe a driver breakup mode, or a diffraction artifact, or a crossover phase anomaly, or a box resonance (either internal or panel). In my experience, sidewall reflection issues skew the image to one side or the other (and often will pull the sibilants to one side of a center vocalsit's voice), but I don't think they tend to consistently localize the sound images at the drivers. You said the center vocalist images very well, which makes me think it's more likely the speakers than the room.

You might try some felt rings around your tweeters in case it's diffraction. Two bucks each from Madisound.

Best of luck to you!

Duke