I think this mirror thing may have originated from the pyramid layout being "upside down" compared with the belt, which was one of the criticisms levelled at Hancock's theory. Menkare's pyramid (the smallest one) is the most southerly, whereas Mintaka (the star it would represent) is the most northerly in the sky.

Mind you, as George said it depends which way you look at it. How do you represent the night sky on Earth, as you see it, or so that each star is "above" its Earthly counterpart (i.e. as a mirror image)?