Hey faninor, I think it's you that's correct on this.
Chris is worried about signal inversion between the two mic sources. A rise in instantaneous pressure at the mic capsule should provide the same polarity of voltage swing at the output of the mic. If they produce the opposite polarity signal from each other, then they are 180 degrees out of phase with each other and contrary to what Chris says, you can't cure this problem with a simple time shift of one of the signals relative to the other. You actually have to invert one of the signals and that cannot be done with a passive mixer unless that mixer uses a transformer for a mixing element. The most commonly used convention is that a rise in instantaneous pressure on the mic capsule should produce a rise in instantaneous voltage at the output of the mic. So, if you send a puff of air at the mic capsule by saying a word that starts with a "P", then the resulting waveform should have a rising edge at the first of the recording of the "P".
So, as long as your mics have the same polarity of output, you should not have to worry about phasing issues if the mics are located at approximately the same distance from the sound source.
As far as placement of the mics go, sound travels about 1137 feet per second. If you are using a sample rate of 44.1 kHz, your Nyquist frequency is 22.05 kHz and you'll get 180 degrees of shift at that frequency if you are just one sample off. Of course the phase shift at lower frequencies for that same time shift is smaller. At 220.5 Hz, your phase shift would only be 1.8 degrees. In one sample period, sound travels just over 3/10ths of an inch, so it does not take much mic separation to give significant relative phase shift between two mic source at the higher frequencies. Then again, your own ears are about 17 cm apart in terms of the acoustic delay from one side of your head to the other. Our brains use that phase shift at the higher frequencies to help us locate the sources of the sounds around us.