In theory, before I put my car on the track, on the starter box, I lean the bottom (LSN) of my engines to the point they start "bogging" and then 1 step back. The top (HSN) needs to sound just a bit rich, but on the track it will be perfect. Ofcourse you first have to maybe run the car for 3 minutes or so, to get it to fully operating temperatures, but then this setting gives very good bottom response and power....
If you use your gas throttle as an on/off switch, the bottom (LSN) should be set a bit richer, but if you have a smooth throttle finger, this setting gives better engine response...