[Kuroshima]

Let's see, the first problem is that If you have, for example, 100 DR (rigid) and 20 DR (flexible) over it, and get hit for 20 damage, a literal reading of the rules would make you suffer blunt trauma, even if the rigid DR could have stopped the damage. This is nonsensical, at no point should adding extra DR cause you to suffer more damage.

The alternatives are making right DR absorb the blunt trauma damage, not allowing flexible DR over rigid DR (problematic, the skull is rigid, and can be under a mail coif, for example), or allowing upi tp "reorder" the DR to make it better suit the situation.