And there is the practical question of "functional encumbrance." Sure maybe you can carry 2 suits of full plate, but if you are moving so slow I can stick a poignard in the visor (or armpit, or crotch), did it really help you? So in our game we handwave stacking; put on a robe over the chain if you want to disguise your armor, but it slows you down enough (+/-) that it doesn't provide the armor benefit that your get from only wearing robe (and receiving the associated mobility).
May not be the most realistic way to handle it, but the only other alternative that we can see is accounting level encumbrance, and that's no fun for anyone.
(History check: I want to say red box D&D handled some items the same way: encumbrance wasn't just weight, it also estimated how bulky and unwieldly an object might be.