I tried messing around with the Witchfinder octave trimpot tonight. Mine was set right in the middle initially. I ended up setting it slightly higher than that, about 1 o'clock. The octave is slightly more pronounced, but there's still plenty of lows. I found the extreme settings in either direction were not really usable, although the maximum setting clockwise is pretty fun if you play it like a guitar octave fuzz, way up on the neck.
