You make it sound as if the Preferred Exit was something "new" added to GSX. It has been like this in years, see the Live Update notes:
https://www.fsdreamteam.com/couatl_liveupdate_notes.htmlIt came in the Aircraft Editor in June 2017, and got another update in October 2017
In any case, you must understand the Stop Position is something that, until YOU set it, simply doesn't exists. It's nothing the simulator knows about so, when you edit a parking for the first time, it's just NOT set, and it would still NOT set unless you move it, even a little bit.
The only thing GSX knows before you start customizing, is the only thing the simulator supports in the scenery AFCAD, which is the center of the parking, so the airplane by default is placed there, and the stop position ( which at this time is still NOT set ) is set to airplane front gear, just to give you some kind of starting point.
About the relationship with the Preferred Exit, is clearly correct as it is. The Stop position it's a position on ground, which will change depending which airplane you'll USE in GSX, which is exactly what will happen in real life, since the goal here is to have different airplane models ending with their own Preferred Exit in roughly the same position, which automatically results in a different Stop Position on ground and that's exactly how it's supposed to work.
Regardless if you are editing or using the parking, you'll see a different Stop position for each airplane ( that's what happens in real life ), but if you put the airplane front gear there, it will end up with ITS own Preferred Exit in the SAME position as the Preferred Exit of the
airplane used to customized the parking.
This way, if the jetway works with the airplane you customized the parking with, you can be reasonably sure ( unless there's a big difference in door's height ) the same jetway will work with any other airplane in use. And that's precisely the reason why there are different stop positions on ground in real life.
Now, whether this would match or not *custom* ground markings on 3rd party airports, it's an entirely different matter, because GSX cannot obviously know anything about how those textures are made/placed and the relationship between meters and pixels across the various stop positions in 3rd party sceneries. In our latest sceneries, like KORD V2 ( but also KLAX ), we made sure our ground markings would 100% match the GSX logic.