I've seen it too, its basically just the cockpit thats vulnerable. I've walked .50 rounds from the tail forward without doing any damage, then *poof* as soon as I hit the canopy. Also put 30mm from 110s and 262s into the engines without smoking them, into the tail without doing any damage, etc.
The Lanc seems a prime example of the key being shot placement, not round size- which isn't right, because a 30mm in the wingroot or tail should do a heck of a lot more damage than a .50 or .30 into the cockpit should.