Best to consult a lawyer my understanding:
Just because one pays real estate taxes in FL does not make them a citizen there. Where you file your federal taxes is important. Good idea to file a declaration of domicile with FL
Northern states have been challenging FL residency for those who claim dual residencies for, well, decades. They aren’t inclined to let their state income tax, inheritance tax etc. fall by the wayside. They have auditors who are very good at their jobs.
Where ever you are registered to vote is indeed a prime determining factor, along with your DL & vehicle registration/insurance. Your ‘home’ bank branch & whether you use the FL address is another indicator.
You generally have to be able to prove you physically lived in FL for 183 days to avoid paying (state income) taxes in another state. As in keep a log
There are other methodologies out there but, IMO, it’s up to Universal to post whatever criteria they want to use in order to obtain a discount.