Problem with a little slipping around is that on long or rough couintry rides, you can get cinch galls pretty easily. A lot of folks try to fix the problem by just tightening the cincha more and then the saddle slips around, the cincha follows and you get a gall.
Kudos for trying to fix the problem.
There is also the method of covering the entire back with talc and then sitting the saddle on and see where it is hitting by the impressionon the talc.I have never had much luck with that,but some cliams it works.
I have never subscribed to the thoery that you can fix ill fitting saddles with more padding
