The marshaller will always guide to align the reference point of the airplane with the center of the parking, which is exactly the same spot as if you were using the "Go To Airport" FSX menu to position to the same gate.
Whether this will result in the jetway connection or not, changes depending on many factors, like the airplane reference point, its distance to the main exit, and the position of the jetway in relationship with the parking center.
But it any case, it's not a GSX issue, because if that jetway, with that specific airplane on that specific parking spot couldn't connect when following the GSX marshaller, it will be just the same if you positioned the airplane using the FSX menu.