I've owned my SC for over 7 years. I should know this by now. But...
Do the auto headlamps come on sooner if you adjust the appropriate dial all the way up, or all the way down? Playing with it at dusk never seems to make a difference for me.
The auto-on rotary knob's range is only for the delay for how long they stay on after shutting down the car - max is 3 minutes. As long as the wheel is rotated into the range/any position but off, they will come on when the sensor detects a specified drop in available sunlight.