The -ar option allows to modify the value for the sharp angle detection. By default it is set to 45°. This means that we dectect a sharp angle at the interface of 2 boundary elements if the angle between their outward normals is greater than 45°.
For example, we represent figure 1 the ridges detected by default (which is equivalent to the -ar 45 option) and figure 2 the ridges detected by the -ar 70 option. The main differences are located at the lid handle.