well i tried something smart today after still having a horrible image despite the L/R EQ centering exercise- it was somewhat OK with TA off but not so good when TA was turned on- and I have grown accustomed to the TA.
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on a curious note, several tones in the upper midrange spectrum just would not center- and even seemed to get louder on the opposite side than the side i was boosting- many tones also started to "ring" and present a second tone on top of the first that also seemed to be on a different side than the non-ringing tone. i assume these were all cabin reflections- what does one expect trying to play musical tones in a small glass cubicle (from the arms up anyway).
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regardless, i just re-centered all of the EQ levels and made them flat. since the original TA shifted everything too far to the right, i decided to give DEX's very smart internal brain another shot at getting the TA and image centered correctly- but played a little trick on it.
I made a "crash test dummy" out of pillows and a sleeping bag and a roll of shop towels for the "head". I tie strapped the mic to the vertical roll of shop paper towels which was set on the top of the "dummy". Before I did this, I carefully measured where my nose (center) and ears were using some reference measurements from the same surfaces of my car. I then put the mic on the dummy to represent where the center of my ears would be.
Because the original TA placed the image way right, I moved the mic center on the dummy a full 12" to the right of my previous autotunes when the mic was strapped to the center of my headrest. The 12" shift was an attempt to reduce the relative output of the passenger side speakers and increase the driver's side so as to shift the image to the left from the previous autotunes.

Well I it rip- still cracks me up that you need to operate the controls and read the faceplate when it's facing ceiling of my car- and I hoped my dogs would keep quiet and that no planes or trains would come by to upset the autotune.

When it was finished, I hopped in and checked out the results. Once again, the autotune really lowered the subs level drastically, but that was easy to fix. a week later and i can rip through the DEX's menus pretty well.
The new image was now to strong to the left- I had made some progress but overshot the mark. Easy to fix? Hope so.
I replaced the crash test dummy and this time moved the mic 6 inches toward the left, biasing it 6 inches to the right of the autotunes I did last week-end. Let it rip, and voila! The new image is nearly dead center! It sounds GREAT! I drove around for an hour playing tunes and am quite pleased with the results.