I suspect there is a varient based on your opponent's ranking vs yours.
When my bro promoted last season, a lot of time his full house was written off as due to the fact he jus promoted. This MIGHT be true and I might be completely off tangent.
However I feel that it has to do with his team's rank being a lot lower than all the other teams in the league. Hence more people came to watch the games.
Now that his rank is more or less on par or higher, his attendance has dropped.
Thoughts?