[PvK]

Except... not.

Full Plate of Ulm is actually 1 point of protection weaker than Black Steel Full Plate. In all other stats it is the same.

So if you put Black Steel Full Plate on a unit with Full Plate of Ulm (e.g. Black Lord or Lord Guardian), the total net effect is +1 to protection.

littlemute is incorrect that stats go down in those cases.

What I imagine he saw was the effect of putting Black Steel Plate (not full plate) on someone with Full Plate of Ulm. In that case, protection will go down by 5, defense will go up by 4, and encumbrance will go down (though cavalry is different from infantry for encumbrance).

That's because "Black Steel Plate" is only a breastplate, so it's much lighter than a full suit of armor.

PvK