Alex_00's page

As far as I can tell RAW should be separate checks for each distraction. Though there is some debate as to whether combat casting should apply to more than just the roll to avoid an AOO.

In actuality I think you have a strong point that multiple distractions make it harder to concentrate that once, and it is silly to make multiple rolls as you couldn't actively concentrate multiple times in that time period and very few other instances involve multiple rolls of the same kind for a single action.

I think that would technically be a house rule. But two ways to do it for me would be to choose the maximum base (10 or 15) and the maximum variable modifier (for instance double spell level). Or choose the maximum base and add the two variable modifiers (so in your example 3x spell level). The latter is probably the way I would go.

It has profound effects though. For instance, if you rule that combat casting only ever effects the cast defensively roll then this would make the feat more useful. If you rule that combat casting affects multiple rolls then folding them all into one makes it much less effective.

"Combat Casting only applies to the specific check to avoid an AoO which is what "casting defensively" is. The other concentration checks are not casting defensively so the modifier does not apply."

I would challenge this. The text of the Combat Casting benefit is:

Benefit: You get a +4 bonus on concentration checks made to cast a spell or use a spell-like ability when casting on the defensive or while grappled.

There are quite a few possible interpretations of this. For instance, you could claim that until you have passed the casting defensively concentration check you are not casting defensively. I think this would be a harsh interpretation and would say you are casting defensively and then checking concentration to see if the spell succeeds. You could also claim that any subsequent checks (for instance for ongoing damage, a triggered readied action or in the case of a full round casting time a usual attack or other circumstance) are "concentration checks made to cast a spell or use a spell-like ability when casting on the defensive". In fact, I think it's a rather flimsy argument to suggest these are not included.

What I would say is that it seems unfair to allow you to 'cast defensively' when not in a situation where you would reasonably fear provoking an AOO or when you expect to be attacked while casting. Otherwise with a sufficiently good concentration bonus there would be very little incentive not to always cast defensively. For example, including the +4 for combat casting my 9th level oracle (Cha bonus +8) has a +21 on concentration checks and cannot fail to cast 1st and 2nd level spells defensively. At 10th level this will include 3rd level spells. There is therefore no reason not to cast defensively even if I'm sitting entirely safely in my bedroom.