I like this idea, Roy...........adds a touch of exclusivity, and acknowledges the artist's original vision of the piece, size-wise, as with an original painting on canvas = one size !!
(are you disallowing cards, therefore? hope so. that will cut that chance of a buyer chopping up your image to their own taste, via that 'customizable' card order offered here - MY very own pet peeve,lol [harmeless opinion]....I do not 'allow' cards now)