I'll still need to modify or acquire a suitable cover plate with all the shifter positions.
A quick check using CaniOn and it looks like the difference from B to C is about 10 kW in regen power, with B having the strongest and C the least regen. Normal D right in the middle of those two. Letting the accelerator pedal go at 70 km/h gave about 10 kW regen at C, 15 kW at D and 20 kW at B. I finally have the low regen "C" option for cruising long distance. Good times!