Alright it's time to talk about cities and what they are to states. How do they work? Well I have two versions. The fusion and the shared body.
Austin and Texas: Texas and Austin share a body because Austin is Texas's capital. In a sense he is kind of his heart or center. The problem with them is that because they are so different from each other that Austin is now his own personality in Texas's body. This is an extremely rare case and is only possible because Austin is Texas's capital. Capital's usually agree with their states so there is no need for another possible. Not so with Austin. I support Austin. Keep it weird.
With non capital cities it's a little different. Cities exist within states of course, they are what make up the states and they use fuse together cleanly. However, if a city is big enough with enough personality that clashes with the rest of the state then it can tip the power balance greatly. Illinois and New York for example are dominated by Chicago and NYC and so they often act more like those cities. On rare occasions they can briefly force those cities out into their own bodies. They are able to do this because they have high enough populations and strength that can support a personification.
The reason why Austin can't be personified outside of Texas is because, he's kind of powering him as his capital? Taking Austin out of Texas might not kill him, but it would not be a good time for him.
Think of it like this. Regular cities are parts of a brain, making up your personality and reactions to things. Sometimes one portion of the brain is bigger than others and as such can send out more signals than the rest. Contrast that with capitals, which are more akin to the heart, pumping blood throughout your system and keeping you from dying. Personifications work on a different level and this is a weird metaphor but that's the gist of it.
Florida and California are a little different. We'll start with California.
California has a lot of large cities, but they blend together easier, and because there are higher proportion of large cities there is more balance. What isn't balanced is what region these cities are in. I see Cal as a mixture of NorCal, SoCal, the bay area, valley, and yes, even Jefferson. SoCal though has a lot of strong personality, so sometimes California's personality can be influenced greater by SoCal. Which is how you get stuff like "Beach On, Beach Off." Usually though, California finds a balance between his different regions.
Florida and Miami's situation is a little more different. Miami's personality is not so different from Florida's own, it's just more Spanish. When Miami appears it is Florida basically calling on the ultra Hispanic powers of Miami.
I don't even know if this makes any sense lmao. I had fun thinking about it though.
(Wow I wonder what would happen if somebody wrote a fic about NYC getting separated from New York and suddenly New York's boyfriends being nervous about if New York likes them without NYC or vice versa and which one of them is even their boyfriend or if they both are. Or conversations about Austin's place in the dynamic with the boyfriends. Hm somebody should write this.)