Ok , I agree with the BMW drawing although yours and mine will be different, the locations look familiar. I don't know the Ci set up but I have never had any water getting into the actual car cockpit, only the soft top stow away area, served by the drains. This stow away area is not carpeted either.
Ill send some pics so you can see the differences and the drain points as best I can identify them.
It sounds like you have water getting into the main cockpit of the car, especially if you have to lift carpet as described in your missive. Never had that issue.