I'm trying to obtain a realistic position for the stairs to exit 1 on the CS_B777-300ER_GE. At present the stairs are being positioned by default half way up the open door aperture.
This is absolutely normal, for an airplane that is still not configured, so GSX will try to guess the door position from the aircraft.cfg, which is not precise.
I've tried editing the setting by adjusting the numerical figure and also using the 3D configurator in the aircraft customisation menu, exiting the program via "save" or "Y" does not alter the stair positioning.
That's not normal. Regardless how you change the settings (typing numbers or editing in the 3d screen), the settings will be changed when you save the airplane. Have you tried "Restart Couatl" AFTER you SAVED the changes ?
Reading this thread I've double checked that there is no gsx.cfg in the C:\Program Files (x86)\Microsoft Games\Microsoft Flight Simulator X\SimObjects\Airplanes\CS_B777-300ER_GE root folder.
This is not relevant at all to your issues. The issue with a gsx.cfg file in the main airplane folder, is a suggestion we give to users that have made some kind of mistake editing an airplane that is ALREADY supported by GSX. If they mistakenly put the gsx.cfg file in the airplane folder, the "Reset" button won't work.
But this doesn't apply to your case, because you MUST create a custom configuration (since the airplane is not internally supported), so ANY custom configuration you made, that will end up in the %APPDATA%\Virtuali\GSX\Airplanes folder, WILL always take precedence on everything.
Despite checking and reinstalling the latest Live update and using reset in the aircraft customisation drop down Couatl menu in FSX Add-ons there is no B777-300..... folder in %appdata% aircraft.
That's normal, of course. You are not supposed to have a file there. That folder will contain a GSX.CFG ONLY if you made one, using the airplane configuration editor AND save your settings. Since you said yourself that you HAD such folder, and you remove it, to re-create the file, you must use the airplane configuration editor AND save your settings.
I don't have that %appdata%\virtuali\GSX file path the GSX installation created a C:\Users\Ian\AppData\Roaming\Virtuali\Airplanes file path.
See above. If you never customized an airplane, there will be no such folder.