Thanks Cassius.
You’re right, I can solve this problem another way.
The script Align to Path works but the method for altering the path after you’ve set everything up seems very buggy or does not work in my experience.
Or, like you say, coping a path into the position value but I find that the path often comes in misaligned and is also fiddly to alter.
I was just hoping this would be a simple very editable way of tracing paths, so that when inevitable changes come in I can just move a few nulls around.