[SuedodeuS]

It's understandable to want to maintain the order of armor layers for purposes of realism, but to do so you need to think of things a bit... differently.

To treat Blunt Trauma as damage rather than injury is simple - for crushing, BT is a special damage type that ignores flexible armor and has a x0.2 modifier regardless of hit location. Injury rounds down. BT is a special linked effect that only comes into play when its "carrier" is stopped outright - and you only roll once for both (use the same value; for BT sources other than crushing, the linked BT effect is actually at half effectiveness).

Now consider 16 falling damage when you are wearing a DR 16 helmet. The helmet stops crushing damage, but as it's considered flexible here the linked BT damage ignores it. Now this 16 BT damage reaches the skull, which is rigid DR 2. It is reduced to 14 BT damage, and with the multiplier this is 2.8 injury. Round down to 2.

The effect is the same as if you just counted the rigid DR first, of course, so for simplicity you can get away with doing that. This exercise is simply to show how you could keep layering in mind without making it overpowered (treating the BT injury as damage to be reduced is overpowered in my mind, as it makes flexible-over-rigid more effective than rigid-over-flexible, despite this not realistically being the case - at least to my knowledge; it also makes every flexible armor foolishly designed, as making 1/6th of the DR rigid wouldn't make a huge weight increase or mobility decrease yet make the armor completely rigid in terms of functionality).