So your gap is on the inner portion of the fender as it curves around towards the grille? If so, this is to allow for the hand finishing of that portion of the fender, including letting in the "notch" that corresponds to the swage line on the outer side of the fender. A certain amount of body filler needs to be built up for this hand finishing, and the final contours should mate with the edges of the chrome headlamp surround.