Acoustic guitars will have a similar proximity effect at the sound-hole; extra "bass", which sounds more like very low midrange in the "chest" region of tone (200 Hz-ish). This can produce a sort-of percussive effect, not what you'd hear from an acoustic guitar.
First, here's the raw, unprocessed recording of a nice acoustic, about 12" away, taken from a single track of a multi-track production:
Note the percussion, due to real low bass near the sound hole. A simple 80Hz high pass filter was applied. Note how the guitar now sounds a lot more natural:
Here is a classic big-head banjo, about 18" away, taken from a single track of a multi-track production:
So, to get more natural signals/recordings, back off.
Here is a video of an original song composed and performed by Karl Henricksen on acoustic guitar and singing. This video uses direct audio from the RM1 prototype shown, synced with video from an inexpensive point-and-shoot camera: