There appears to be an issue with the spawn radius settings for player controlled planes and UAVs. Currently, entering a plane will virtualise all units regardless of spawn radius settings (excluding civilians and compositions).
However, connecting to a drone will cause units to appear "normally" (it's unclear which spawn radius is being used at this point, presumably the UAV's though). You can disconnect and reconnect to a drone while seated in an aircraft, causing nearby units to despawn and spawn accordingly.
Helicopters appear unaffected by this.