It's a bit of an edge case.
Specifically, with these settings for a custom post type:
'type' => 'file', 'force_delete' => true, 'upload_dir' => WP_CONTENT_DIR . '/resources/',
File deletes as expected when deleted from CPT edit screen, but if the containing post is binned and the bin emptied, the uploaded file remains. I can write a hook if you could suggest the best action/filter, but was wondering if there are any other parameters that can be passed to ensure the file is deleted?