I heard this from a ma'amar back in yeshiva, but I cannot remember the source. In Ezekiel's vision of the merkavah, the supernal "chariot," the face of the lion is to the right while the face of the ox is to the left. Obviously, the lion should be on the left and the tame ox on the side of chesed. It's explained in Tanya, igeret hakodesh 20, that the spiritual worlds are like an inverted seal. So too, the merkavah is also reversed, but I can't recall the source.