Very helpful Peter – thank you. I had “browsed” that paper in the Journal but clearly missed the vital bit which was of relevance to my recent sunspot adventures. Quite a difference between the two groups in Fig.24, is there not? Good to know that I wasn’t just doing something silly with my analysis though and that at least smaller sunspots really do move around. Maybe fortunate that my second subject for analysis (2835) was exactly as per your description of the ideal candidate else I really would have been puzzled!
A good learning experience though, so definitely worth investigating.