I've tried all different distances from the microphone with the same results each time. The only real way I have to measure the output is by using the Arduino's analog ports, and seeing the size of the waveform in terms of the numeric distance from silence. In all cases, the distance has been too slight to be of any use.
Specifically, I was trying to experiment with the uSpeech library, but it interprets everything as silence. That's when I wrote code to actually look at the output to see what was going on.