My players want to use our current location (Reading, PA) as our in-game city, and we only have around 80K people in the area. Even with a smaller-than-metropolis population, we can still see a laundry list of reasons and explanations as to why there would be a frakton of supernaturals in the city. I don't know if this population record includes the surrounding locales that are often clumped with Reading when it comes to mailing, such as Mount Penn, Wyomissing, Shillington, etc (each of these locations being more suburban communities outside of town than actual individual cities).
Additionally, I remember in other RPGs (I think it was the old World of Darkness line) that the "average maintainable" status quo was something akin to 100 mortals to 1 standard supernatural. Sure, while this means there can be 800 Red Court Vampires in town, it doesn't mean there needs to be. At least with this idea, I can feasibly say that in this general area of Reading, I can have one Black Court Scourge at a college campus and another at a blood bank, a White Court family with three households across "town," a few minor talents and Red Court Infected skulking with the gangs, and no one would be the wiser.
Personally, I think it's the HOW you blend in everything than the how much, especially with how "easy" it is for some of these entities to come in via the Nevernever.
Just my two cents, don't mind me.