Hi Tom,
Here is an alternative, I believe that Dynamic and Simulation have their place, but I think a simpler and more controllable solution is better here.
The idea is to have a Spline defined (which you might have already) and use this in a Volume setup.
CV4_2025_drs_25_ANfg_01.c4d
This allows to define and animate the "thickness" of the material while animating a Spline Interface (see image)
Screenshot 2025-01-10 at 10.17.15 AM.jpg
This allows for a very fast animation setup.
An SDF Dilate Erode can be set up for a Global size change to create an even more detailed setup for the animation.
The cube is there as an example that the solution can be defined by a geometry Context (subtract)
Let me know if that works for you.
Cheers