The only thing you can achieve in the GSX editor regarding jetways, is to HELP GSX detect if there IS one.
Sometimes two gates are close and the jetway for the parking nearby might be closer to your position than the correct one so, by editing the parking position in GSX, you are just HELPING GSX to *know* if there's a jetway or not, but nothing you do there will ever affect how the jetway *WORKS*.
Jetways are not handled by GSX, and are not called by GSX. Even if you have a jetway option there, it just sends the standard key command to the sim to ask for a jetway, exactly as if you were using the default ground services, because GSX jetways in MSFS *ARE* default jetways, just with different models, which have the same exact measurement as the original ones, and are placed exactly in the same position as the default ones.
This means, if a jetway of a particular gate worked with a particular plane parked in a particular position in the default scenery, it will work exactly the same in GSX and, the opposite is true, if it didn't work in the default scenery, using GSX and customize anything in the parking spot, won't change anything, the jetway still wouldn't work, because the default jetway animation system which even GSX jetway use, doesn't know anything of the changes you made with the parking editor.
Of course if you edit the GSX STOP position and, because of that, the jetway worked better because you now parked the airplane in a new position according to that, it's to be expected, and it would have happened just the same, even if we didn't replaced its model.