Does not detect all files generated by custom post type

I have tons of images in /uploads folder that are linked to custom post types. Quite common actually. The custom posts is generated by another plugin. In anyc ase, the smush pro does not seem to detect a single file outside of Media library.

Understand the reasons behind only using media library but it is preferrable to use uploads directly for large sites without needlessly creating database and application overheads.

It would be great if you guys could tell me how or bugfix this option.