It should work in the extra user folder as far as I know, so we'll investigate this after the Easter holidays
Have you tested it yet by chance?
I reported this issue a few times years ago, that the addon structure didn't work in the user-defined folder.
IPACS eventually agreed it would make sense, but I don't know if anything has been implemented yet.
I stopped using the user-defined folder for that reason.
The clumsy scenery structure should definitely be avoided, only leads to a mess.