Frost Presence, Toughness (Frost), and the Austere Earthsiege Diamond armor
multipliers apply to non-bonus armor. That is the base armor that you would find on any piece of gear that *normally* would have armor (i.e. head, shoulder, cloak, chest, bracers, gloves, belt, legs, and boots).
It does *not* apply to "bonus" armor which is the *bonus portion* on any armor number that appears green (you can find the base armor value on any other piece for the same slot that has the same ilvl and subtract the difference which is the bonus portion), and
any armor that appears on your neck, rings, trinkets, weapons, or special procs. It also does not affect armor gained from Agility.