Just cause the guy is standing in front of a Cobra, doesn't mean he's the crew chief, or even the gunner. He might have gone out on patrol right after the shot was taken, or may have just returned. Right now, or surely when the picture was taken, there is no "up front" relative to that base. Note the sign labeled Taliban pointing in all directions. Unless you think Khe San wasn't "up front" either? What they have is an airhead, analogous to a beachead, but with no nice big comforting grey ships visibile, just a few helicopters, not enough to lift them all away at once, should things go to sh**, not I that I think they will.