Wow, you must have a lot of dust there
What you could try, is to get winamp 2.x with the MAD input plugin. Play some tracks with point source sounds which are shifted significantly, but perhaps not entirely to either left/right. Then go to MAD properties and invert left/right channels. This sound will now play on the opposite side of the stereo spectrum, and in optimum conditions it should sound exactly like the original.
If it sounds noticably different, either in tone or stereo localization then you have an obvious problem.
Also, I noticed the volume trim on the YSMs is not calibrated correctly. So a -6dB on one may represent a -4dB on the other or so. At 0dB, both of mine seem to be correctly matched, but if I take both down to -6dB, one is notably off-volume to the other, significantly shifting the stage. So if you can tell center-stage is off, trimming it will fix that. In your case however, I'm almost certain the wall is causing all your problems. It will distort the notes coming out of this left speaker which in turn will make the sound stage fuzzy. I'd get it out of there as soon as possible. It's not necessarily too bad if the speaker is relatively close to a wall, as long as both are symmetrical, or the same relative distance from their walls. What really matters is not how far the speakers are away from the wall, but how far you are from the speakers in relativity to the wall.
I measured mine to be almost exactly in the center of the room. They are each 4' away from side walls, 1.5' away from the rear wall and about 1.5' away from my head.
The rear wall isn't much of a problem as long as the side walls are relatively far away because the sound still has a lot of cubic area to dissipate behind the speaker.
Also it would help to have them near the front of the desk rather than at the back or somewhere in the middle. That will reduce desk reflections which can as well be pretty significant given it's proximity to you is closer than the speaker itself.
If you have a monitor in the middle, its important that the speakers not be behind it. Either on the same depth as the monitor or in front of it. And check that they are symmetrically in the same position, including rotation. What seems like an insignificant imperfection can break the sound stage. Our ears are sensitive to phase, tone and volume when determining sound location. Phase distortion will make focused sounds appear to come from both speakers. Tone distortion will blur the sound stage and volume will shift it. A small change of around 2dB to one speaker will shift the entire stage over 30 degrees. That's pretty significant when you're in close proximity with high separation.
Perhaps some tweaks seem isnignificant in themselves, but it adds up. TBH when I first got the YSMs I wasn't overly impressed. My experience was limited and I didnt really know what I had to do to get them to sound right. Over the last year I've been gradually making tweaks and adjustments and now they're nothing short of amazing. Just recently I got a new parametric EQ and a ratshack SPL meter
. Which showed me that my bass response was severly disfigured. Even with a subwoofer I noticed that I had a sharp rolloff below 50Hz to nearly dead-zero at 20Hz. I was getting severe cancellation with the subwoofer in that particular spot. So I moved it around, cancelled the peaks with 5 high-Q bands and now my response is SPL meter variation aside, 20Hz-100Hz within +/-2dB, and thats in-room response, which is pretty spectacular. Anyways, point is little things make a difference and they will add up over time, its just how well you know your room and system. I think you'll get to like them much more over time, they only get better for me.
