pillars-of-eternity
I have equipped my rogue with a bunch of a nice items offering an attribute bonus. Yet when I check the character sheet, I get the information that some of them are suppressed yet it is not explained why.
It be great to know how the item bonus stack or are suppressed.
In my case it looks like this:
I've marked them in red on the map here, they're just behind the wolf that attacks you:
The answer to your question, and the answer to your problem are two different things I think.
Damage Reduction seems to not be taken into account when dealing with Damage Over Time effects. I would be more certain of that if I had more than one DoT spell to hurt my team with, but Concelhaut's Corrosive Siphon dealing supposedly Corrosive damage works the same whether my character wears +6 Corrosion DR armor or not.
In Combusting Wounds case... Directly testing it is impossible, it doesn't hurt allies. And however I look at it, the description seems wrong. If it were a DoT effect, we're lacking information about one time - either the time over which that 5 damage is distributed, or time the spell lasts.
What follows is a baseless conjecture
It is possible that this 5 damage gets lost - if it really is DoT it might (extrapolating from my experiences) apply wrong amount of damage, and disappear the reminder if timer is not in the correct by-3-divisivness. Or it might have a long timer (in the realm of 9 seconds, which would be about 2 per 3-second period), and not stack which would fit your experience of unimpressiveness.
Any way I look at it I think we will hear about DoT effects in patch notes sooner or later.
Best Answer
I don't believe you can stack effects via items; 3 items with + might will only confer the best bonus of the three. Your only way to gain better bonuses is to find an item that has more of that particular stat.
Supposedly (according to the manual) rings stack, but I don't feel like that's been my experience. (edit: rings should stack with other effects, but not with each other)