Black Monks :
You get matched with people the same number (similar) of fans as you. So there is a chance that your number of fans are higher than most in your championship and thus you will struggle to maintain fans. I feel it's one of the things the developers did a nice job with. However, i am staying at lvl 20 stadium simply to avoid the issues with fans that come at 21 & 22.
There's some top level players doing the same and thisnis resulting in a hit of an inbalance in the fixtures. There's nothing wrong with a lvl 23 or 24 player having a stadium of 140k but because a level 30 or 31 decided not to up his stadium it is causing these lower level players to face stronger opponents.
Its not the norm and something that wont be resolved easily but it does unfortunately happen.