Check my math if I've missed something, but if you have 18VAC (L-L) at the alternator, and
line volts = rms volts/ph x 1.732, and
DC volts = rms volts/ph x 1.732 x 1.4, therefore, you should have about 26VDC at the 100 rpm pace.
If so, you would expect to see a cut-in voltage of ~50VDC at 190 rpm. I think this is close to what BRC is suggesting.
If the first of your 16 steps is at 140V, it is way too high. I'd suggest your first step be -0- amps and voltage close, but a bit above nominal battery voltage, then ramp up - going light on the amperage settings for the first few steps - from there. The last step can be somewhere near your max amps, and your Current Limit in the Classic should be at or near the same. The mid - to upper stages can be adjusted, but I think you need a starting point.
I would double check the Classic settings, that you are configured for 48V, and getting this to the Classic - I believe you said this is your bank voltage, correct - 10.6V sounds too low for the standing voltage. I'm thinking ours is in the mid - to upper 30-volt range.
~ks