I had always heard or learned that it was behind rather than in front. However, a google search finds two definitions as being the "point where the base of the forward slope can be seen without defilade" [dead space] so I probably was at least partially incorrect. However, depending on the steepness of the slope the military crest could be behind the actual crest if the slope were not severe. Personally, if someone were shooting at me, I would rather be behind the actual crest.

Randy