Don't forget you can always check yourself using the ADE or AFX programs.
Or, you can just *trust* GSX...if it's saying a parking is too small, it's because it has compared the actual radius as specified by the designer in the AFCAD, against the wingspan of the airplane you are using.
Note that, this is exactly the same rule the default ATC uses: if a parking is too small for your airplane, the ATC will never give it to you.