Say, there is a unit wearing Gambeson, whose value for Mass is 1, and Heavy Mail, 3.
According the text, the resulting mass is calculated like this; (0 + 1 + 3 ) ÷ 3 = 1.3
BUT, say, there is a unit wearing only "Heavy Mail"; (0 + 3)　÷　2 = 1.5
A unit wearing only Heavy Mail is lighter than the unit wearing both Gambeson and Heavy Mail, which doesn't make sense to me.

I wonder what the reasoning behind this is. Or maybe I'm more terrible at math than I expect.