So I opened your last 3d model, and see that the "Beam" is indeed that area.

So you have 2 large surface to define your detail area. use trim on the fender twice, once with each of the large surfaces, then remove them and the cutout.

Then use blend on the 2 edges, and crank up the "Bulge amount", to generate your detail. (You will need to trim the one edge down with the other before the blend. You'll see)

Tangency will be more forgiving. With curvature will generate sharper creasing. If you needed to use G2 or more, make your cutout LARGER.....

Hope that helps.