Is There A Known Cap For Def Down/Def Ignored?

I lack the resources to just go out and test this myself at the moment, but after looking at how the update has changed some things I have to wonder about how DEF down works. For example, is each source additive or multiplicative? Can you in fact manage to get to 100% def down or ignored?

I was looking at sources to try and figure out how much attack I would need to cap against various targets, and I realized that increasing my attack was much harder than simply lowering my target's defense. Just a 900skill frailty and dia 3 would be 44%. Since my LS frequently uses PUPs, Armor Shatterer lowers DEF by another 16%. So now we have -60% Def if they are additive. Triple Fire Attuner ignores 45% def against normal mobs, and 22.5% def against NMs. So if I have dealt with 82.5% of my target's DEF, what's really left?

Someone has speculated that End game mobs might have 2500DEF+, but if we are bypassing 82.5% of that, they have 375def left. My regular attack puppet with no buffs has 1500atk. I could probably cap at that point.

But I don't know if this is viable due to not understanding how DEF down works mechanically. Can anyone explain it?

Isn't it possible to reduce to 1? I know from being hit by Intervene (at least from AA Elvaan) that Attack can go that low, so it'd make sense if Defense did too. I do know you could test it in Ballista with Bolster Frailty + Angon or whatever else Defense Down crap you can pull, though I guess the question is more a matter of whatever enemies are subject to the same minimums we are?

In terms of multiplication, I'm quite certain that the values from each source are added. For example, if you were hit by Defense Down -20% and then Dia 2 (-10%), you'd be at -30%. However, if you were then given Idris Indi-Barrier (+85.8%), you'd be at +55.8% Defense.

Berserk (-25%) + Aegis Schism (-75%) puts you at 1 defense, and I see no reason why enemies would be any different. Also I miss the Ashu Talif.