Puzzle: Do Bosses keep some Armour when "Fully Broken Armour"

some days ago someone took me, once more, with him to the "King in the Mists" cruel2 and cruel3.

being fully physical damage, and not having crazy gear, i expected to basically deal almost no damage.

but here is the thing:
i do expect my damage was that low, so it was reduced by 90% (max value by armour negation). i basically did 1pixel per hit (not kidding). but then fully breaking his armour should have increased the dmg by 10x, and adding another *1.2 multiplier for a total of 12x dmg increase, yet it didn't seem to do anything, at all.

my weapon has a base dps of 520.41, not counting accuracy dmg-bonus or crit chance or that.

i keep thinking about how that is even possible. even if my dmg was that low, a 12 fold increase should have been noticable anyhow.

the only idea i can come up with, is so the in-game tooltip is missing this most crucial info, and we cannot actually reduce a bosses armour to 0.

it also would make sense so we can not increase physical damage by a 12fold, since we can't do that with elemental dmg either and the elemental skills don't deal crazy more dmg than physical ones as a baseline. yet the game itself tells you otherwise..

thoughts pls? i really am puzzled by this experience.

addendum: funny enough, i still was able to facetank the King's tornado + him smacking me + frogs solely by leeching my way through without even moving, at all. how can i get such good life leech when i deal like 1pixel per hit.

something very odd seems to be going on.