[Varyon]

Not really. The "shared housing" that, say, two layers of mail would have would be in the form of buckles, straps, and perhaps padding (I'm not certain if the weight of padding increases as armor gets heavier/thicker, but I kind of doubt it), and I doubt those amount to anything approaching 20% of the weight of the armor (and certainly aren't 20% of the cost). You might be able to get a little weight saving, but it's probably all beneath the resolution of the system.