ps: we usually use MxMP instead of diff for armor by piece.
Do you mean you only apply 3*MxMP
No. Armor maneuver penalty x3 apply and instead of a difficulty staging we use MxMP (it's the same for armor sets but it differs a bit to armor by piece)
And studded leather ... "Rigid Leather, Hard Leather (including
armor made from furs and hides), Studded Leather,
Brigandine Armor, Scale Armor (leather)"
# it is what it is: rigid
# have you ever tried to swim with wet fur worn?
# metal studs or lames ..
# interlocking metal plates ..
# shaped metal pieces ..
But if you need leather armor for a sea campaign, special crafted with a reduce xx to swim penalties (houserule?)
Otherwise use ML (p. 45) and a superior workmanship bonus (decrease MxMP and MnMP) or special materials. (ie integrated hog-bladders** inside the leather armor)
** correct expression?