i would think running a-b would neutralize some or most of the color the mics impart to the sound. most of the microphone color is due to differing frequency response when the mic is off-axis. certain frequencies become emphasized and others diminished, creating a distinctive sound to the mics. when on-axis, the mics typically have a flatter frequency response resulting in a more neutral sound, i would think. but i have never run a-b so take it fwiw.