Here is something quick and dirty. I didn’t bother to sweep the rectangles, just lofted them. Part of the trouble now is that your surface is so convoluted and unrealistic.
beam_sweep_2023Mar3a.gh (21.1 KB)
P.S. Replaced Loft with Sweep 1 using isocurves (purple groups). No difference?
beam_sweep_2023Mar3b.gh (25.3 KB)