One can't give a firm opinion without a photograph of the whole space, but on rule of thumb, a mantle picture is usually best hung no more than a few inches above the mantle, and pictures hung as a pair should usually also be hung close together -- three inches or so. That said, the picture above my mantle is a full 24 inches above the mantle (and quite small) -- the setting just forced me to ignore the rules. That's where it looks best to me. (Don't tell any other Houzzers.) :-}