GSX doesn't "load", so it doesn't have the concept of a loading range, except for JETWAYS, IF GSX jetways are in use on a certain airport.
JFK loading range has obviously been carefully set to be lower than other FSDT sceneries, because of its close proximity with other airports ( LGA and EWR ) and the Manhattan skyline so, if we tried to load it earlier, it will likely crash FSX and 32 bit versions of P3D4, and will still down fps a lot in P3D4, so the range has been chosen to be sure LGA won't be loaded together with JFK.