I suggest reading the chapter at Page 39 of the manual named "Understanding the Stop position", which explains how, by setting the stop position you'll achieve this automatically, since GSX gives preference to the airplane "Preferred Exit" which will end up always in the same position, resulting in its front gear placed differently depending on airplane type.
The goal here was to end up with the exit in a predictable position, to ease up jetway solving.
Yes, it would be nice to possibly customize this further (it will be a chore, though), and having custom sub-stop position adjusted by airplane type too and in fact, GSX can do this already, internally ( we used it on some of our airports, like KLAX ), but we'll need to think of a user interface that is not too complex to use, to allow user customization. Is not trivial, our internal system can even take into account the pixel/meters ratio of an eventual custom ground texture with the airplane stop markings.
