The complicated issue is that options 1a to 1d, which are the park options involves building on an unstable unregulated council tip. As LLAL was handed free land maybe that would persuade them to overlook the obvious dangers. The existing project to upgrade Luton to 18 million passengers is already over a year late and is 70% over budget. Not a good sign for the future.
South is best but not in LLAL's eyes as there would need to be over spill into the Hertfordshire badlands even if it was just for airport parking.