The UV map for the brows is skewed a bit, or rather, to be more exact, one of the brows is rotated a bit. If I place the exact same brow on the map, flip it and make the inner starting points at the same relative location on the UV map, one of them will come in at a different angle than the other. It's not necessarily a bad thing, because it means brows , as on real people, won't be identical, but it is something to keep in mind if you want more symmetrical brows.