Oh, good catch about the 900k! That gives us at least something to go by. Do we think all Dixingren are registered, or only the ones with powers, or ...?

What really eliminates Dragon City from the 500k max category for me is the scenery we see from the University roof.

I just rewatched the rooftop scene in episode 1, and it honestly doesn't look that huge to me. The roof isn't high enough to see very far, and the view reminds me a bit of one close to my current home.