First, let's be particularly clear what A, B, and C are. Are A and B the blue irregular curved distances? Is C the distance between the midpoints of the two short straight segments?

Is B the outer blue trace or some linear distance related to that?

Is A the inner blue trace or some linear distance related to that?

C appears to be the linear distance between the midpoints of the two straight segments and the straight segments are included in neither A nor B?