So, it begins to dawn on me that CI is related to SPEND on Advertising. Nothing to do with how well I run the airline, or age of aircraft. Just Money Money.
A year later and I still haven't found quite how this works out as I tend to small and medium planes, 20 to 70 seaters, and find CI's of 20 to 30 are fine if there's no serious competition. If I do get into routes between major airports then I'm going to get hammered if I don't keep the planes on that route up to standard, protecting the RI rather than worrying overmuch about CI. This will usually happen when the bigger players have filled the big routes and are looking for profits on the next level down and with money to throw at taking command of those routes.