Sorry, but I believe even the manual is wrong on this one. I play a lot of head-to-head games against myself to see how certain things work. I was playing an Axis night attack, maximum visibility of approximately 198 meters, with mud. As the Soviets, I purchased AT and AP mines, no Daisy Chains. During the game, as the Germans, before my soldiers stumbled into the minefields, several of the fields were spotted, one as far out as over 150 meters. None of the Germans triggered the mines, and as the soviets, none of my guys had moved and could not have triggered them. From everything I've seen it is completely random. Additionally, my Germans were running when they spotted the mines.