Hmm, apparently "hide and ambush" doesn't work in all situations. I only just recently began trying the tactic, but it does seem to help. I.E., if I had one of my anti-tank guns just hide, the enemy was on top of them before they knew it.
When I set an ambush point several hundred meters away, the hiding gun crew "unhid", and began firing at a Sherman as soon as it crossed the ambush point. So at least in some situations it helps to counter the spotting penalty imposed by hiding.
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"Follow me, and I'll show you where the iron crosses grow"