Played with this value on my An-2 on the windshiled My observation is that at value 0.1 the plane unflyable - even maintain altitude and/or speed, so it's not fully clear for me too I've used 0.01 steps to show icing on windshield, placing 10 transparent (0.05%) layers before the windshield (outside) Here is a video, attached the ratio to throttle for testing