Nowhere in my post did I make the assumption that the armor was hollow. If anything, I assumed that the armor occupies the entire volume of the character.
Again, are you absolutely sure that it isn't negligible?
All the developers that have commented so far have yet to present a concrete example, only hypotheticals, and neither have you. Here are extreme, concrete example I made myself.
Light is a tool with a density of 0.01, Heavy is a tool with a density of 0.7 (Plastic). Nothing is the control. Blocks are 2x2x4
Another example, (EDIT: 100) random protrusions on one side of the character as long as 5 studs, originating from the center. 0.7 density vs 0.01 density.
And lastly, I'm not arguing that 0.01-density will eliminate all negative effects of having large parts sticking out of your character, but in any practical example, it gets pretty darn close at doing so.