Ultimate Facebook comments not showing after activating "Override WP settings"

I want to make the Ultimate Facebook comments the only one that show in the posts.

However, when I choose "Override WordPress discussion settings", neither form shows (nor FB nor WP).

I have tried disabling that and using the Disable Comments plugin as suggested in this other thread, but is the same: the FB comments form does not show up.

So, is either both or none.

Also, is there a way to make FB comments form responsive?

Regards.