I like your idea of rotating the top horns. They seem to be the right length. As for the bottom ones, like someone said, in the concept art they protrude at different angles, and they do seem a bit short. Also the very middle two on the bottom seem to have a little inward curvature on them in the concept art, but maybe that's just me being really picky. Everything on the actual mask looks amazing however, including the paint job. Great stuff!