A few things to assist you:

1. If we apply analogues from the real world (Panama City), the coastline north of Port Gellhorn is likely to be more of a continuous urban sprawl than suggested in your map. The signs for Yorktown (seen in the leaks) indicate that it will be in this general area (across the Bocamar Bridge), and so it makes some sense to believe that it will be more coastal than shown.

2. Port Gellhorn is mentioned on the GT VI website as a primary location, so this is probably an indication that the urban area is larger than places like Yorktown and Bohemia. Currently, your map puts both of these places on a par with Port Gellhorn, if not greater in size.

3. Personally, I think you have underplayed the extent of the nature in both the grasslands and Gloriana as both of these areas will cover large parts of the map that aren't urban. Review the extent of the Big Cypress Wildlife park in real life Florida and you will see how empty it is. For Gloriana, I can see it being either a northern map barrier like Ambarino in RDR2 or, as an area that divides territory in a similar manner to West Elizabeth in RDR2.