At this moment you can’t have an arbitrary pitchbend range. Only multiples of an octave in millimeters. So 230mm is one, 460 is two and so on.
For me personally I don’t really mind the C to B as I’m never sliding that far. I think that a third is about the largest interval that I slide. You could double the pitch bend range so you can do a full octave in half of the width. But then hitting a new note or sliding is out of sync. Or you could edit my file and give it that 13th box :).