I got this question in an international level competition.
I would like to ask this question from Different Free Body Diagrams topic in chapter Equilibrium of a Rigid Body of Engineering Mechanics
To elaborate: The couple is the cross product of the force and the perpendicular distance between the forces. And if the division of the both is done than the resulting quantity is the distance only. But care must be taken that the product is the cross product and hence sine angle must be divided too to get the distance.