There are no catering vehicles in GSX that are locked by the gate radius. Some GSX vehicles are (some Pushback trucks), but none of the catering vehicles is linked to the gate radius so, changing it will not have any effect on the choice of the vehicle used for catering.
They are ONLY dependent on the airplane service doors heights so, the only possible reason why you don't see a catering vehicle, is that you configured a plane wrongly, not setting the service door height correctly.
However, if you set it too low, for example, you should *at least* see a MiniVan, which is the vehicle used in case the service doors height is very low.
So, the only possible reason I see you would see a message about "no catering vehicles", is that you configured the service door too *high* instead, higher than the highest limit for the larger catering vehicle ( the Scania CT-8000 used for the A380 ), which is about 8 meters.
Is the airplane you used is already internally supported by GSX, it should be enough to use the "Reset" button in the airplane configuration page, to restore the configuration to the one that comes with GSX.