Well, that's tricky, he *is* filling his stadium. He not only loses out on income, it will likely also mean his other facilities aren't upgraded as well as they could be, meaning less boosters for him and more injuries (for you too when you play there.) I don't know if or where there is a point that a full stadium wouldn't get you 5%, as I have always upgraded. I will pay attention when I play at small stadia and see if it ever happens.