We have to deal with the cold temps predator hunting up here. For a scanner, I keep it fiurther from my eye. It'll still fog from time to time, but waving it in the air will clear the fog. I haven't had an issue with my MK II, which has a shuttered eye cup, but I'm not looking through it for long stretches.
If I'm using helmet mounted PVS 14s, I used to roll the eye cup up and set max distance from my eye. Ended up liking that so much I just leave them that way.
Never tried anti fog. Will though!
JPK