I've had great success with a pair of SDCs placed in a manner similar to the one you mention.
12th fret and *near* the soundhole are good starting points - but only experimentation and your ear can tell you where the mics should be placed.
As far as the room goes, it's going to affect your sound to some degree, but close-micing will reduce that.
Finally, if you've got the extra channel, and the extra mic, throw a room mic up somewhere. You might find a good spot despite your room.

Hope that helps.

I like using using 2 sdc mics for recording acoustic guitar in smaller spaces. You want to get the mics as close as you can but far enough away to not have boominess or too much string sound. You need to be especially carefully with the soundhole mic, more out near the bridge pointed back to the soundhole not directly in front of it. Of course each situation and guitar is unique and you should experiment to get the best sound. If you have the channels a room mic and a direct (acstc/elec) are also good ideas easier to not use any given track than to be left wishing you had something a little brighter or whatever.

Lots of threads in this forum about acoustic guitar miking - use the search engine.

You have to be pretty careful about using two mics on guitar because of potential phasing problems, unless you use a spaced configuration such as A-B. If you are aiming to capture in stereo the whole instrument sounds, including fingerboard squeaks and the players shirtcuff buttons catching the bridge, as well as the spaciousness of the room, then try a co-incident pair of SDCs or a stereo mic like the Rode NT4. I've also had success with M-S technique using a cardioid SDC (or LDC) as the M and a fig-8 LDC as the S. Many people will put a room (ambient) mic a little way back from the player to blend in at mixdown.

Whether the result sounds good in all its stereo glory depends on the player and also whether it is a solo recording or has to sit in a mix with other instruments. It's crucial that the player learns to keep the guitar still while playing, since any dual miking technique (either stereo or blended mono) is sensitive to movement of the sound source.

I know there are others in this forum who have different techniques to share. Some time ago, Jeremy Cucco [[url=http://[/URL]="http://www.recordin…"]posted [/]="http://www.recordin…"]posted [/]some lovely pics and clips of guitar using a pair of Mojave MA-100s in A-B configuration.

I would like to extend my thanks for the feedback provided. I haven't been browsing this site very long, but have found it to be a very useful resource over the past few months.