Side Mount tire plates

[duke36]

Are the side mount steel plates supposed to be dead flat? I have a pair that have a slight concave curvature lengthwise (from the inside), which appear to conform to the wheel bolt pattern. The concavity is in the area where the arm bolts to the plate, i.e, when viewed from the rear , the arm/bolt area projects out or is cupped toward the wheel in relation to the 3 studs. These appear to be originals for '30 but not sure.