How is the curvature of a unit achieved? If only a slight curvature is needed than the factory will use horizontal stitching to get this. If more curvature is needed than the factory uses darts (over lapped lace) to achieve this. The larger the base size the more contour is needed. A small piece needs only a small amount of contour and sometimes none is needed if the base is really small. Sometimes the factory will use horizontal stitching in the front and darts in back--and vice versa. In the example below the front of the unit is very broad and it required both horizontal stitching and darts to get the right curvature.
Regards,
John