Thank you IPACS for your reactivity!
Autoheight works now fine with airport ground mesh for xref and cultivation buildings (I haven't tested yet with vegetation and lights) of TOC files declared within airport tsc file.
@Scenery designers, please keep in mind that autoheight won't consider airport ground for autoheight calculation of objects declared in separate tsc files, causing then potentially floating/sunk objects.
In other words, keep clear enough from airport zones when placing objects like cultivation or xrefs on regional scenery, and declare everything around an airport within the airport tsc file if any.
Airport creators can then easily extend their cultivation/xref coverage to seamlessly merge with regional scenery...
Remainder : airport ground mesh is not just the strict area containing runways, taxiways and apron, but generally an "island" shape around the airport, allowing for soft, seamless, mesh integration.
Airports creators should ideally share a KML of their surfaces footprint...
Example from the wiki tuto: