[dogscoff]

I can't say for sure but I'm pretty sure there will be no stacking at all under any circumstances. The highest available value is used.

This means the optimal design would be one "scaled armour" (can't remember the proper name) and a bunch of armoured structures. The armoured structures will take damage first (usually, since they have the higher damage resistance) and benefit from the emmissive value of the scaled armour. That will make for a damn tough ship. The only reason to have >1 scaled armour is as a backup, in case the first gets wasted by a lucky hit.