I tried fixed BC, B becomes slack with C still tensioned when depowering. Turning seems slower and less responsive than BC on a pulley. Even powered the pulley will distribute tension more even than fixed.
I have another idea.
Should increase C movement powered and reduce B? Technically B should hold half the tension of C, the actual lengths will be interesting.
I could obviously add more pulleys to the C section and increase the tension on it further. I wonder if this could create a similar effect to a 631 or higher mixer, but with a short throw.