The % is the more important number, the arena size has a lot to do with attendance numbers, a team with a larger arena can have a higher attendance but a lower %, Boston was 14th in attendance but 11th in %, so there were bigger arena teams with a lower % that had higher attendance.
Lets face it, Miami is the land of sun and fun, it's never going to have a Pittsburgh like fan base because there is simply too many options for things to do in Miami as opposed to a place like Pittsburgh or Cleveland where the fans show up no matter how bad the team is, the great weather of Miami that draws some players also has it's cons.
In 2006-2007, the Celtics were at 90%. Then they got to 100% with Garnett and Allen joining the team and have gone to 97% since they left.
So my argument stands. Big cities with multiples teams will see fluctuations in attendance based on the team success, even with a storied franchise like the Celtics.