That's it, thank you Alan! Depending on the circumstance, it seems easier either to use a script that takes NURBS as an input (allowing the user to manually position them) or to use an earlier version of the script that takes polylines and a numeric position for each as the input (which makes small adjustments of position easy from within the script.) On the earlier shelving example, it was quite easy for the resultant curve to crash the contour portion (when the curb doubled over itself, for example) so I spend time, trial and error, moving the middle curve up and down. Fun!