I like to put one mic on the top rotor, far to the right side (away from the motor, back side, covers off), facing straight in, so that it's never directly on-axis w/ the spinning horn. Then one on the bottom, right side, same as above, but not as far away from the rotor. The "mics on opposite sides" technique has never sounded good to me, sound like the rotors are sppinning twice as fast, and too choppy. That's also why I like to mic off-axis, sounds smoother, less choppy. Obviously, for studio stuff, the technique would be different...