Similar Cobb angles clinically may look different depending on curve pattern. All patients on this figure have a Cobb angle of 40 degrees. As can be seen, the more decompensated a curve, the more visible the deformation. Double major curvatures are compensated; the most stable curves present after the end of growth  and therefore rarely requiring surgical treatment.
Weiss and Goodall Scoliosis 2008 3:9 doi:10.1186/1748-7161-3-9