My first reply using Iso Curve was wonderfully simple (version ‘24a’):
In addition to that white group, I needed to override the Rotate ‘P’ input because the Rhino shape was not at the origin. I was oblivious to the fact that isocurves all have the same direction so didn’t see the flip curve issue until later.
But as I said, isocurves are affected by surface shape so they weren’t evenly spaced:
Which led to versions ‘b’, ‘c’, ‘d’ and ‘e’ 
I vaguely recall now that this issue of the top edge plane intersection curve being flipped has been reported and discussed before, in relation to contours.
But I struggled with it yesterday, wasting a lot of time going through four different versions to understand and fix the problem. 
Same flaw mentioned five years ago: