I guess that is very liberal to offer 1/4 of the mug in the name of safety .(I mean HEAT)but you get it.
My thinking is that less sun exposure to the skin and penetration to the inside of the helmet would keep you cooler, and also give you that additional face protection, and opening the vents and potentially lifting the face shield a bit would get you that needed airflow.
But this discussion is like oil and tires, with many options .