Oh. Why not use an Ellipse component instead of going to all the trouble you did?
Anyway, I have other plans today so won’t try to do the spiral in both directions as shown in the image.
The white group that I added is competing with the cyan group to make the tapered surface. Good luck.
tower_2020Dec20b.gh (27.1 KB)
P.S. I think using Loft is making things more difficult regarding spirals in the other direction. Points on the station curves that you are lofting usually suffice.