GSX reads the default so the gates appear up high.
GSX reads both files now, including the elevation correction .BGL. But the issue is, it seems the ones from OrbX are placed in a very low layer, just above the default terrain, but BELOW all the airports.
Since GSX respect the Scenery Library layer priority, it will give the default airport an higher priority, because it HAS an higher priority so, whatever altitude it read from the OrbX altitude correction .BGL, will be overwritten by the altitude set in the default AFCAD, which DOES have an higher priority.
I though it seemed weird to have an altitude correction file below the airports, but another user asked on OrbX forum, and they replied this is the way it should be.
Now, your report seems even more puzzling because, what you did, was to create *another* altitude correction file, not unlike the ones from OrbX, but you placed on an higher level and, sure enough, GSX read its altitude, and everything's working fine.
So, I now wonder why OrbX asks to have their altitude correction files below the airports, since yours works fine. Is your file able to fix issues like the plateau effect on airports with sloped runways ?