Offset on surface goes wrong with list

When I try to make this offset curves, works fine but not for the concave surfaces. I tried making it the “long way” but when I calculate de surface normal on centroid, it gives me a wrong plane, but don’t know how to solve this.

Thank you!


(upload://aR2qnxHQh1gbVfmOxug0iwpq4a6.gh) (7.9 KB) SRF.3dm (131.7 KB)