That's quite simple. Any folder on your hard drive than contains a scenery subfolder containing BGL files (and optionally a texture subfolder containing bitmap files) AND is listed in the Scenery Library listing AND is checked as Active is an Active Scenery Area.The phrase..In active scenery area...has always confused me.
A file cannot contain a BGL file. Thus I assume you mean that IJPFSXLibraries is a folder. If so and it contains the Hobbs _Aircraft.bgl, then it will not load into FSX, since the BGL file is not in a scenery subfolder, which is required. If it is not in a scenery subfolder:The file IJPFSXLibraries, which contains the Hobbs _Aircraft.bgl