How beautiful! I would put a black sashing border around the entire center (same width as the other sashin). Then I would put a wider (maybe 2x the width of black or a little more) of the red in the cardinal bird, followed by a wide grey. The entire set of 3 could be 7" (or thereabouts). If you want to break it up, you could put a corner square of the birds in each outer corner, after the black.