Jed Laurance

I know this is a super late response, but I was looking into the same issue and I figured I should post my solution for posterity:
If you view the dependencies on the waterline parameter on the flip solver, you'll get a big list of parameters that are being driven by it inside the solver. It's a bit tedious, but if you go to each linked parameter and change the drop down to the left from Use Default to Set Always the waterline will update throughout the sim.