I suppose what i would like to do is to start with wall profile curve in plan and then use divide curve and cull points to achieve variable widths arch base points. Group each pair of arch points and find the center. Give the center point a Height in the z-axis and apply a curve through each group of three points.
What I am not sure about is how to then properly harness data trees to group sets of three points?
If anyone has some ideas of achieving this outcome or could give suggestions of yt videos that would be great!