Multiple Characters with Disruptive

[AdAstraGames]

It looks like two characters (A fighter and a Magus) who play together a reasonable amount are going to both end up with the Disruptive feat.

What happens to the Concentration DC if they both flank the same wizard?

Does the DC rise by +4 per person with Disruptive?

PRD wrote:

Your training makes it difficult for enemy spellcasters to safely cast spells near you.

Prerequisites: 6th-level fighter.

Benefit: The DC to cast spells defensively increases by +4 for all enemies that are within your threatened area. This increase to casting spells defensively only applies if you are aware of the enemy's location and are capable of taking an attack of opportunity. If you can only take one attack of opportunity per round and have already used that attack, this increase does not apply.

The fighter will also have Step Up & Strike as their next feat, and has Combat Reflexes. Does the AoO from Step Up & Strike and any damage that may result from it increase the DC of the spell being cast? I could see the argument going either way:

PRD wrote:

Benefit: When using the Step Up or Following Step feats to follow an adjacent foe, you may also make a single melee attack against that foe at your highest base attack bonus. This attack counts as one of your attacks of opportunity for the round. Using this feat does not count toward the number of actions you can usually take each round.

Normal: You can usually only take one standard action and one 5-foot step each round.

Argument For: It's an AoO that interrupts a target's 5' step and cast action.

Argument Against: It's an AoO triggered by the 5' movement, not the spellcasting itself, and would no more trigger a damage concentration check than if the caster did a move action and provoked the AoO rather than the 5' step.

[GeneticDrift]

I believe unnamed bonuses stack

Step up applies after the move before the wizard has even thought about what to do with his remaining actions - so he can cast as normal, he does risk a second AoO if he casts a spell next to the fighter.

[Wizarddog]

First off, Step up & Strike is not a AoO per say, because it is just an intermediate action the fighter can use that uses up a AoO. It is triggered by the 5' movement, which has nothing to do with casting a spell. Because it is not an attack of opportunity, it won't effect concentration. Damage only effects if the target provokes from attempting to spell cast or from ongoing damage.

Regarding the issue of the DC of Distruot, Bonuses without a type always stack, unless they are from the same source. However, these are increases in DC that are the same type but come from two different sources (2 different PC'). IMO It could go either way but I favor placing the +8 DC squarely on the caster.