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Windshields (auto glass)...as with all (most) body design features are not "mathematical".It is"developed" geometry. Yes, whilethe corner radii "cuts" can be true radii or some type of conic, the spline they attach to will likely not be anything "ruled". The overbuild technique is sound but watch your final shape cut(s). Auto glass is formed while hot and thus has unique edge conditionsthat usually flow non-normal to the A surfaces.