I have a general understanding what causes attendance to go up and down...but is it determined by raw numbers of fans or percentage of capacity?
I see the % stat, so it makes me think that, for example, a poor fan survey might cause your next home game to drop by 10% instead of X number of fans. If that's the case, then it makes sense to keep building the arena, even if you're not maxing out capacity. A small slice of a bigger pie is still more pie. Mmm... pie.