Re the 'demarcation line' - my understanding, simplistic as it may be considering the real world doesn't act like a textbook, is that the flow of air over a ridge or hilltop can act something like airflow over a wing; ie conforms to the curve for a while, and somewhere behind the point of maximum curvature, may unstick and become turbulent.
So, Overt Auk, if you crept up to the hilltop shallow or level from the downwind side, you would be in the turbulence and downdrafting. If you came in at an angle on the steepish side of normal going to a pad at the top of the hill, you should be out of it - if this concept is appropriate for the conditions on the day, of course. Or you could approach across wind if the terrain allowed, in which case shallow might well be fine too.
Naturally everyone can think and do what they want; it's just one way of looking at it that I think is reasonable under some circumstances.