Slant 6 Exhaust Manifold Washers

Thats correct. When the manual says "cup side against manifold" they mean the concave (think 'caved in') toward manifold mounting ears. They could have said "cone side out to nut" and made easier sense of it. If you dont have the special serrated nut (flexloc ? FLEXLOC) that nests in the brass washer, you could use more triangles at the ends as that's what they did in later slants.