Hi Richard -
I went to the Search Index being used, it originally had the Standard analyzer and the Search Preview seemed to be bringing up the expected results across all search modes. I did as you recommended, switching to the Subset and rebuilding the index. It doesn't appear to have any effect on the search on the site, still getting no results on any search other than "Any Word", even if it works in the Search Preview. Nothing in the Web Part settings seem to jump out as an issue.
I'll continue to experiment with the other settings, but still looking for ideas. I very much appreciate the response though!