Magic damage taken question

[Sady]

This might sound silly, but I figured I'd check with the math gurus. How exactly do MDB and -% magic damage equipment/traits interact?

My understanding is this, please correct me if I'm wrong. The "cap" is -50% reduction. Shell accounts for about half of this so you try and make up for the last half from gear. Beyond that, you go for MDB gear in remaining slots to further reduce damage taken.

Say I have -18% and +16 MDB (on RDM so add another 12), assume -25% from shell. If my math is right, I'll take ~45% of normal magic damage.

100-18-25 = 57
57 / 1.28 = 44.5

Does MDB allow you to, in a sence, "break" the 50% damage reduction cap or is this setup overkill?

Edit: Added math blurb for clarity.

[rog]

that's pretty much correct.

keep in mind that if the mob has any mab, then you'd multiply by (mab/mdb).

for example, if a mob does 100 dmg with 20% mab, then base damage would be ~83.

83 * (1.2/1.28) = 77.8
77 * .57 = 43.89

in this case, you'd take one less damage than if it were just 100 damage with no mab, however with higher numbers, it can definitely make a more significant difference.

[Suiram]

Does MDB allow you to, in a sence, "break" the 50% damage reduction cap or is this setup overkill?

The cap isn't on overall reduction in damage. It's on shell and shell-like gear specifically. So you are correct in that combining them would yield less than 50% of unbuffed damage. To see why there's a cap on the one and not the other, examine how much damage you'd take if you added say MDB+20 to the hypothetical you gave, compared to if the game let you add 20% more magic damage reduction without a cap.

@Rog, mob MAB is never actually going to make a significant difference. At most it will be only a few points of damage difference. Even in the example you gave, the base damage for a mob doing 100 damage with 20 MAB would be 84, not 83 (floor(83*1.2) is 99, floor(84*1.2) is 100). With 84 base, the damage after MAB/MDB it works out the same as the case with 100 base damage and no MAB.

[Byrthnoth]

You're eating a 1000 damage nuke naked
= 750 damage taken with -25% Magic Damage Down (Shellra V for simplicity) = -250 damage, 25% lower damage taken than Naked
= 500 damage taken with -50% Magic Damage Down (Shellra V + Aegis) = -250 damage, 33.3% lower damage taken than -25% MDT
= 396 damage taken with -50% Magic Damage Down (Aegis + Shellra V) and 26 MDB (Unfettered Ring, Ataractic Solea, IR Dastanas/Hose/Sallet, Lamia Mantle +1, Lamian Kaman +1, Resolute Belt, Volunteer's Ring) = -104 damage, ~20.8% lower damage taken than the -50% MDT
= 793 damage taken with 26 MDB (Unfettered Ring, Ataractic Solea, IR Dastanas/Hose/Sallet, Lamia Mantle +1, Lamian Kaman +1, Resolute Belt, Volunteer's Ring) = -207 damage, ~20.8% lower damage taken than Naked

So -MDT gives increasing returns, MDB gives decreasing returns (26 MDB = -20.8% damage), and they're unrelated.

It's not much of an issue for Paladin as far as I know, but you can use INT to reduce the damage you take from most nukes as well. It's not as efficient as MDB or -MDT, and the only time I'd actually consider it is with Duelist's Gloves +1 on RDM.

[Sady]

Yeah that's what I thought, just wanted some confirmation. Thanks!