On my watch, which is on default text size, the first two blocks on the left are filled in. If I look on my phone, the circle is on the second notch from the left.
I've not noticed it changing the screen brightness at any point in time. If it has, it certainly is not nearly as noticeable as it is on the phone or the iPad. Without an auto setting, I'm inclined to think that it just stays at whatever brightness you set and will not change unless you modify it. Maybe in future firmware updates?