Robertson, Walter? - portrait of a man in brown coat

This is possibly by Walter Robertson, as the miniature does appear to be similar in style to his other works, although smaller in size. 1438

However, there is a miniature of similar smaller size, and in similar pose depicted in the catalogue, American Portrait Miniatures in The Metropolitan Museum of Art, as fig. 80, Portrait of a Gentleman, ca. 1794, which is attributed to Walter Robertson.