Problem with autoreimport

I have been trying copy fbx files directly into the folders and have UE4 ‘autoreimport’ them. I know I’m not technically ‘RE’ importing these assets but a setting in the editor preferences leads me to believe that this process should work for new assets(see attached image.) When the engine asks me if I want to import the new assets it doesn’t create any actual assets in the content browser. Is there a special workflow for importing directly like this? Is there a limit on how many fbx files can be imported at a time?