cowitness and lower 1/3rd only mean how much of the viewable area of the optic is covered by the iron sights. Seeing as the red dot will follow the location of your eye (when parallax is removed), this is a physical attribute and is independent of the actual dot itself.

cowitness (aka: absolute cowitness) is when the iron sights take up the center of the optic.

lower 1/3rd is when the irons take up the lower 1/3rd of the optic.


The concept is that it's easier to view the dot when there aren't a big set of irons in the way.