i believe they flip one of the primary discs so that the connection goes S-F-S-F
instead of S-F F-S like the stock model,
the discs are wound and varnished, then they slide them over the core, so you can have a reverse wound primary disc simply by putting it on backwards and swaing the leads.
why they did this i do not know, having them assembled with on flipped would cancel some input noise and any phantom switching would push the coils towards each other and cancel mechanical motion,
the way EMI switched it, both coils would move in the same direction but this is damped out with the rubber bumper at the end of the core.
maybe hi end was improved by flipping the coils as capacitance to ground would change,
or maybe negative feedback is changed, as when those discs move to one side, you are losing a bit of flux as the energy is turned into mechanical motion. this results in a little loss of signal at the low end as the discs are too heavy to respond to hi frequency motion.