This is not a problem and it's exactly how GSX is supposed to work.
As explained in the manual in the chapter "Understanding the Stop Position", GSX has a completely different concept of the Stop position than the sim, which is very limited and based only on the front gear, which "looks better", but it's not really realistic, since the front gear position is never the same for all airplanes.
GSX, instead, has the Stop position to be a value independent from the front gear and, instead, is based on the Preferred Exit, so when a custom Stop position is made with GSX, it will take the Preferred Exit as a reference, so different planes will end up with their Preferred Exit in the same place ( which makes the Jetway connection more predictable ), and *naturally* have their front gear in different positions depending on their type, exactly like in reality.
And yes, this requires setting the Stop position, usually in the place where the Jetway ( is present ) works, and once you do that, you can be reasonably sure the jetway will work with almost any airplane, because all of them will end up with their exit in the same place.