I have question. Are the faint lines that appear in the borders of the middle patch (created by a sweep of one curve and two edges as profiles, with tangent option activated), a result of imperfect tangency or simply the outcome of having a second surface created inside another one?
If I were to manufacture that part would those lines be there?
Yes I realize that I can trim that patch a notch lower with 2 curves and then blend but I think that creates a tiny, tiny buldge plus the edges on the vertical sides create a small opening that is quite visible even with an additional cut and blend.

Thanks