The disparity has everything to do with your room and set up, I'm sure. I have the same problem (imaging left of center) and I believe it's largely due to the unsymmetrical nature of my room layout. In particular, I have an entry way directly behind my right speaker. If I stand in the entry way while music is playing, it's clear a lot of musical info, esp bass, is going into that space.
I highly recommend getting a copy of Jim Smith's Get Better Sound. It's invaluable. For speaker set up, they need to be equidistant to you, and also equidistant to the center line that runs from the front wall through your listening chair. This is measured down to fractions of an inch. They also need to be level. FYI I found it very useful to use some yarn as a measuring device. Tape it anywhere on the center line, and use it to measure the front and rear corners of each speaker and adjust for both distance and toe in. Works great and no need for any sort of ruler. However, it may be impossible with your room and set up not to have to use the balance control.
I highly recommend getting a copy of Jim Smith's Get Better Sound. It's invaluable. For speaker set up, they need to be equidistant to you, and also equidistant to the center line that runs from the front wall through your listening chair. This is measured down to fractions of an inch. They also need to be level. FYI I found it very useful to use some yarn as a measuring device. Tape it anywhere on the center line, and use it to measure the front and rear corners of each speaker and adjust for both distance and toe in. Works great and no need for any sort of ruler. However, it may be impossible with your room and set up not to have to use the balance control.