Wow! You never take time off, Umberto. I didn't expect to get an answer from you until Monday.
Just to clarify, I place gsx.cfg files in %APPDATA%\Virtuali\GSX\AIRPLANE_NAME only. I haven't touched any other location. And my FSX is located C:\FSX and not in program files directory.
Several attempts but all have failed. When I set the position of refuel point visually using your "editor" and then restart GSX, it should work, right? Well when the fuel truck comes it positions the worker and the connector about 4m above the wing above where I have saved it. When I go back into editor, sure enough, it has added 4m to the vertical component and visual editor confirms that 4m above position. And I thought that the coordinates that show up in aircraft editor would correspond to those in the gsx.cfg file. Problem is that they do initially, but as soon as I call for fuel, GSX lowers the vertical by 3.54m. If I restart GSX and again call the fuel truck without any further editing it subtracts another 3.54 from the vertical component displayed in the gsx.cfg file. When the vertical gets below 0, the large fuel truck no longer deploys but the old "shell" truck and it positions itself in the old default position next to the left wing. So something definitely is not right. I will go back to the PMDG 737-800wl again and see if similar is occurring.