That's why I think it's always good to start from scratch (don't throw in big, and especially third party's, tgc's) and build up the main structures first, then start to define smaller elements.
The numbers, btw, are just altitudes. With each smooth step, you make a step; first between 20 and 20.5m, so half a meter for a rather flat (it would be ugly if you make it zero, I think) bulge-in edge. In the upper it's a softer 25 to 30m step for the wall to bulge out again. And the warping makes it go up and down of course. You can even make some sort of stairway like this, with a distance shader set as warper/vdisp input.