I just installed a set of P90 pickups in my new Casino Coupe guitar. They are Reverse Wound, Reverse Polarity to each other, which is supposed to give hum cancelling in the center switch position. Well, it does, but only if BOTH pickups are at the same "level". In other words, if both pots are full on: hum cancelling. One full on, the other slightly lower: hum. Is this how these are supposed to work?