Thanks to all for all these helpful comments. My SCT is a non edge c11, bought new circa 2013. It is a hyperstar compatible one. I bought a feathertouch focuser and Microtouch controller from Starizona a few years ago when I visited the U.S.
SGP is really useful and comprehensive software - I use it for all my imaging sessions, so trying to get the autofocus to work effectively with my kit is something I have wanted to do for a while.
As a result of the posts in this thread, I have now got to a definitive position which is completely reproducible - thanks to all who have chipped in.
I find these settings are good
Backlash compensation set to IN and value 800
In settings I use 7 points of 40 steps each.
I obtained reproducible curves on 10 attempts tonight, whereas in the past my curves were a random set of points which I always had to monitor.