On Holley type carbs with the level plugs, the fuel is just starting to trickle out over the bottom threads when the level is set properly. I'm not sure how much bigger the sight glasses are than the plug, but halfway up is way high, as suggested above.

When I am doing a quick and dirty fuel bowl R&R I turn the bowl upside down and set the top of the float parallel to the top of the bowl.

R.