Reading Anthony Beevors D-Day I have come to a conclusion on this map: the height map is wrong. Mortain tuns along rhe pass between hills 285 and 314. Abbey didn't have 76mm guns, but "a platoon of tank destroyers with 3 inch guns". Then again, it could be an error in translation, as I have the finnish bias translation of the book. I will see if I can find out more.