Eugene,

The 30 mil bias must always oppose the 60 mil neutral loop.

In spacing (no current in the neutral loop) the 30 mil bias pulls the polar relay to spacing.

In marking (60 mils in the neutral loop) half of that 60 mils counters the 30 in the bias winding, which leaves 30 mils to pull the polar relay to marking.

So the effective 30 mils each way should create no distortion going through the polar relay. I also believe a properly adjusted polar relay is bistable (which would not matter in this situation.)

Tom   N3CRK