The thread is old and it looks like the new Relevanssi version doesn't have a way to change "All public post types" to "Everything". At least, I can't find it.
I have 2 search boxes:
1. Blog search. When I use it I get this kind of URL: http://site.com/?s=term, but it also displays matching custom post types.
2. Custom post types: http://site.com/?s=term&post_type=product
It displays only custom posts, as needed.
Any way to fix this?