GSX Jetways are a 1:1 replacement for the default Asobo model, both in size and placement, which means using the same airplane, on the same gate, in the same position, would have resulted in exactly the same situation because, as you can see from your screenshot, the jetway is already completely extended, and it would have been wrong if we removed any constrains, resulting in the jetway breaking up in pieces.
The issue is, the default jetway animation system is quite limited, and allows jetways to dock partially, when it would probably be best if that jetway wouldn't even move, so you would know you parked a bit too early for the jetway to reach you. GSX doesn't change how the jetway animates or work, it uses the default system, just with better looking models.
What you can do with GSX, is to customized the STOP position, to have GSX guide you in a positions where the jetway would reach the door, in that case a few meters ahead might have been enough. The Parking customization editor has a TEST function ( NumPad5 while editing the Parking position ), that will try to move the jetway and, since the STOP position is related to the Main passenger exit, once you tried with a certain airplane model that it works, you can be reasonably sure it will work with other airplanes as well, since in presence of a custom STOP position, GSX will guide every airplane to have its own Main passenger exit ending all in the same place.
