This is the explanation that went with the instructions:
"The middle position leaves the lower diode disconnected, eliminating the octaving. One of the side positions connects the diode to restore octaving, and the other side position disconnects the lower diode but also bridges the upper diode to effectively remove its impact on the circuit, giving a less "reedy" distortion."
But hey my prime goal here was to get rid of the octave so I'll stick to that and that only.
So if I understood correctly it would look like this: