I already gave my airline and marketing information at my initial post.
Sorry missed that. That level of spending will probably take you to about CI of 40
I will agree with the initial company image boost you said. And i guess it is fixed at level 20. However, it is not linked with any marketing campaigns or it seems like that.
Yeah, it seems it acts as a temporary, artificial floor, to help out starting airlines.
Just imagine your real (not artificial) CI starting at 0. It would grow slowly, over time getting to 20 and then exceeding it to go higher.
I previously operated an airline where i had no marketing campaigns since it's start and for a long period of time, probably months. The company image was at level 20, stable. Than i decided to start a marketing campaign and company image started to rise.
My guess is that company image starts at a fixed level (20) and stays there whatever campaign you have, until a fixed period of time since the creation of the airline. Than, should you have a marketing campaign it rises. But it does not fall.
You can definitely exceed it.
I don't remember now if there is a difference between starting the game world on day 1 or later, when game is already in progress. When you start late, the system awards you some boosts in some categories (RI on first routes, some passenger level expenses are reduced). CI boost may be part of the package.
I seem to recall that when you start on day 1, CI starts at 5, and you exceed (when marketing is in effect) that level fairly quickly, and you see the rising CI.