In my room, I measure the distance from each speaker to the exact center of the listening position to within about 1/8", and then fine-tune the exact distance by ear. That helps, as there's an optical illusion in my room that makes the right speaker look closer than it is.
In a previous room, I was getting the image pulled to one side despite all my careful measuring and wall treatments. By chance I found that a vertical cabinet edge well off to that side was the culprit. Sound was diffracting off the corner, which was acting as a secondary sound source. I would hang a little damping material on the cabinet when I listened, and the imaging was vastly improved (especially on close-miked vocals. I can't stand it when the sibilants come from a different point in space from the rest of the voice). You might have someting similar going on in your room - you might try draping a thick towel over various pieces of furniture to see if you can find the culprit.
Well assuming that doesn't help, I would suggest you use the balance control rather than positioning one speaker farther than the other, because you want to preserve the timing cues that would otherwise be skewed if you moved on speaker farther away.
In a previous room, I was getting the image pulled to one side despite all my careful measuring and wall treatments. By chance I found that a vertical cabinet edge well off to that side was the culprit. Sound was diffracting off the corner, which was acting as a secondary sound source. I would hang a little damping material on the cabinet when I listened, and the imaging was vastly improved (especially on close-miked vocals. I can't stand it when the sibilants come from a different point in space from the rest of the voice). You might have someting similar going on in your room - you might try draping a thick towel over various pieces of furniture to see if you can find the culprit.
Well assuming that doesn't help, I would suggest you use the balance control rather than positioning one speaker farther than the other, because you want to preserve the timing cues that would otherwise be skewed if you moved on speaker farther away.