Where do you have the mic pointed? I have used the NT1-a on both nylon and steel stringed acoustics and, IIRC, had the best luck getting a good sound out of each with the mic around 12-14" away placed around the 14th fret and slightly angled away from the soundhole. It took some playing around with though and my room was untreated so it may be a completely different scenario for you. Good luck!
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