It’s not about a specific shape, it’s finding the real existing thing in your object and depicting that in the illusion of 3D. Maybe the U but it’s “coming at you”, so have some extra paper and work out the different strokes.

The best way I have had cross contours explained to me is: imagine you are running your finger through the subject and replicate its dips, valleys, and peaks with the stroke of your pencil or the value you are creating. So you want to have your crosshatches to visually represent the volume while also doing the value work.

Pop open a charles gibson image or look at other artists famous for crosshatching and look at how they did clothes.