Question regarding stacking IT:DR

[Phantasm]

Say I have three characters, a tanky brick, a melee DPS scrapper, and a buffing caster; Brick has IT:DR /5, Scrapper is just wearing light armor. Just before a fight the Buffer casts a spell which grants IT:DR /2 to all allies in an area (bypassing armor because Malediction).

Does the Brick take the better of the two, are the two IT:DR numbers added or multiplied, or does his own IT:DR go up a level to /10? (Obviously the Scrapper is glad to have the increase in case he accidentally grabs aggro.)


Likewise, is "Cannot stack from multiple castings" a +0% Feature or a -5% Nuisance Effect?

( The current build I'm working on: Affliction 1 (HT+0; Advantage: IT:DR /2, +500%; Area
Effect: 8 yds, +150%; Cosmic: Bypasses DR, +300%; Emanation, -20%; Fixed Duration, +0%;
Reduced Duration /2 (1.5 minutes), -5%; Requires QN Roll (Own Roll), -10%; Selective Area, +20%;
Sorcery, -15%; Alternative Ability, ×1/5) [21] )