Other spots that seemed large enough to park a Captain Sim B777 in GSX will tell me that it cant operate in that spot because the aircraft is too large.
But that's not obviously a GSX fault, it's been clearly explained in the manual, and can be easily fixed in the GSX parking customization page.
As explained many times, in the forum and in the manual, GSX doesn't know anything about the outside world, other than the AFCAD. If a parking space *looks* big enough, but the scenery designer has decided to define it smaller than it is in the AFCAD, GSX doesn't have any other choice than to trust the AFCAD, perhaps the designer used the size as a way to prevent certain airplane types to go there for some reason.
But using the GSX parking customization editor, you can easily fix a parking (or a group of parkings), overriding the radius as being set in the AFCAD.