thanks for your answer. But is there a way to assign a different stop position to every aircraft type separately?
There's no need for that, because this will automatically result from the fact that GSX used the preferred Exit as a reference, so it will try to have that one always in the same position, which will result in different stopping positions on ground, meaning the front gear will be in a different position for each aircraft.
What you will have to careful with, if you have a parking that can be used both by small and heavy airplanes, with the heavies using the 2nd door for the jetway, is to be sure that, when you customize the position using the 777 with a preferred exit as 2L, you place enough ahead so the position of ITS preferred exit ( L2 ), should be good for the exit of another airplane that uses the L1 as preferred exit, that's why we also put two dashed lines over the preferred exit, as a reminder.
The main reason of using this method, is that you can use any plane to customize a parking and, if you head the "ding" sound when testing the jetway on that plane, you can be reasonably sure it will work with every airplane, and you don't *have* to set a separate stop position for every airplane, which would result in 10x more work when customizing an airport.