Nap of the earth isn't always right if you fly into the wrong valley.
I flew the same route on successive days with two different pilots. One, by the book, crested the ridge at the prescribed minimum before pushing and descending into the valley.
The next day the other pilot skimmed the ridge well below the min altitude, I could look in to the door of a shepherds hut. He then descended below the valley tops but some 900 feet above the bottoms.
In the former case we would have been dead meat to a ZSU23-4 or SA. In the latter we could have quickly moved over the valley side to the next valley.
Read the terrain.
Another example, the planned track had us climbing over a ridge. The next map sheet had a Fan Song radar nicely placed to catch a ridge hopper. Flying around the high ground avoided early exposure.