The idea that the ES charge is concentrated at one area on an LP or on the mat is contrary to data collected by Shure Corporation, when they studied ES charge in vinyl reproduction, albeit many years ago; they suggested that charge distributes evenly across an LP surface. However, I could perceive that there might be some assymmetry to charge distribution due to fingerprints or other oily or watery deposits on the LP surface. So perhaps the data you cite would contradict their earlier findings. I will take a look.
How does a static charge and electric field manifest itself in the signal?
And we still have not had an answer as to whether the 18Hz high pass filter on the preamp was engaged during all of these investigations. If it was engaged, then I would expect there to be little to no woofer pumping when the platter is spun at speeds below 18Hz. Yet I thought the OP reported he can spin the platter by hand at speeds well below 33 rpm, and still visualize the phenomenon.
If it was say the magnetic field from a Hall effect sensor or the motor, then as long as the thing is localised to a small fraction of a rotation, then it will appear like >18Hz.
In XLR configuration, positive attaches to Pin 2, negative to Pin 3, Pin 1 is vacant and the shield is attached to the shell. The shield is floated at the TT end.
^As you have said^… that is pretty much the main difference, and hence why I suggested that you could try attaching Pin-1.