After two attempts to bend the Masonite around the sharp bend shown here, I realized that what was possible when bending it one way (back side out) is not possible when putting the front side outward. Then I spied an errant piece of .060 styrene that just happened to be the exact right size! Trying it in place, it conformed to the curve easily, and the PL construction adhesive firmly attached it to the backing Masonite. Problem solved!