I just did a bit more testing, and I think I figured it out - the "File name / URL" parameter only checks for the literal name of the file - it ignores the path to the file. Fair enough, makes sense.
My Windows color theme prevented me from clearly seeing that the comparator for the "Full file path" parameter is actually a "contains" and not an "Equal to" . I guess that solves my issue, which ended up being a bit different from the OP after all. Whoops. That's why I thought that to get a partial match I had to use "File name / URL". Maybe those characters can be bolded in the UI for better clarity?