Cyo premium sensor?
 

I can't notice any difference at all on my Cyo Premium main LED whether it's on "S" or "T", the 2 bottom center LEDs are brighter in "T" but that's all. Could be the sensor is covered somehow? Where is it located?

It is hard to tell the difference, but you have it figured out.

In "S" mode daylight the DRL operates at full output, and the main beam is dimmed. In the dark the main beam operates at full output, and the DRL is dimmed. Its really only noticeable from the saddle if you enter a tunnel from daylight, then you will see the transition.

The sensor is under the rotary switch, and is exposed by the cutout in the "S" position.

Thanks kickstart, I thought the difference was huge, looks like it isn't so.