I'm in this fairly small dungeon blasting away at some Marauders with my Flare spell and I keep hearing them say things like "Damn rats." etc. like they don't know I'm there. It should be pretty obvious that I'm right across the room, it's really not a very big one. What game setting would I need to adjust to make them aware of my presence? I think maybe I'd like to double the range.

PS: So I just came across fDistanceInteriorReactCombat and the exterior version. Would those be the settings? I suppose I could just try it out, but if someone could confirm I'd appreciate it.

No, that's not it.

fDistanceInteriorReactCombat is the distance at which a hostile actor (NPC or creature) will attack, but only if the actor has detected the player.

FDistanceExteriorReactCombat determines the same for wilderness encounters.

If they're still saying things like "Damn rats. etc.", it means they haven't detected your presence yet, so changing those settings will have no effect. I once got very close to 2 bandits, sneak killed one and the other just stood looked at the dead body and said "Must have been the wind.", meaning he didn't detect me even though I as right in front of him (and no, I wasn't using chameleon or invisibility, just sneak).

Check out this http://cs.elderscrolls.com/constwiki/index.php/Category:Detection It has a lot of detail on Detection and what influences it.

It kind of looks like fSneakMaxDistance is what I'm looking for. Unfortunately I've already killed those Marauders in order to test it out. It was in Fort Nikel where the Bandits and Marauders fight each other, and everytime I'm there I think about how silly it is that I can be right across the room and blast them with my Flare spell without them knowing I'm there.

You'll find that happens in pretty much any dungeon. Half the time I'm not even sneaking and I can blast them with my spell without them knowing I'm there. It really gets me when I blast one, and a second one just stands there until I blast him too. I'm not sneaking! If I want to fight them in melee, I have to run to within a few feet of them before they see me. This seems to be a real weakness in this game. I guess that's why so many have tried to tweak the sneak settings and what-not. I have no idea what the settings would be if you're not sneaking.

Yes, fSneakMaxDistance is the setting. I'm back in Fort Nikel and after doubling the value, the Bandits across the room now detect me when I hit them with my Flare spell. I'm going to try with only 50% to see how that works.

PS: So a 25% increase was all that was needed, at least for that area. Anything below that only had one of the two Bandits responding to my attack. The default value is 1500, I now have it at 1875 and they're both taking action.