This is a design trend I've been trying to make happen for years. I love chunky frames on tiny art! I think it makes the most impact if the frame is a flat panel style or mostly flat.
Below is a 6x4" acrylic original. A woodland scene in a distressed barnwood frame. And I recessed the art with deep spacers (no glass) to enhance the window effect.
And below here is a 12x8" prematted souvenir print in a spectacular Isabella frame. Deep spacers also used here for a shadowbox look. The art is a miniature print of Hieronymus Bosch's Garden of Earthly Delights which is a very detailed and fascinating piece of work. If you have never spent time lingering over this triptych, get on it. Necessary viewing.