Create loading substate for application

I'm trying to create a loading substate for the Application route using the new named substate options added recently, but for some reason, I can't get it to work. Originally, I just had created a simple template, loading.hbs, and it worked automatically, but because of the issues with substates on the application route, some of my UI was still visible. I'd like to correct this now.

I've tried renaming and moving the template around to the following places:

/templates/application_loading.hbs 
/templates/application-loading.hbs
/templates/application/loading.hbs

None seem to work though. I don't need any custom routing behavior so the default generated route should do me, unless its a requirement for this to work. Documentation on this feature seems to be sparse.

Thank you for any assistance.