All these addons have not been customised by me and are using the built in GSX settings.
That's the issue, without any customization, GSX will place the center of mass of the airplane in the center of the parking spot, just like the sim would have if you were an AI. This because by default, it's the only information GSX has on a parking.
Note that, this is exactly the same if you use a Marshaller or a VGDS, the distance/deviation calculation are exactly the same.
To make a proper customization, you should change the GSX STOP position ( which is a GSX-only data the sim doesn't provide ), in a way that is more correct for that airplane compared to the rather generic center of the parking.
I suggest reading Page 43 of the GSX manual, the chapter named "Understanding the Stop position", which explains in more detail how it works, and the relationship with the airplane exits.