I am a keen horse rider and getting tight in my inner thigh is very common. I do this exercise and it makes a tremendous difference to my pelvis position, gait and to influence how the horse can lift its shoulders and back beneath me.   

The intention here is to improve the ability for your femur to move in relation to your pelvis. Reduce an anterior tilt if you are lordotic in your back or reduce a flat back if you have a posterior tilt of the pelvis. The difference between the two is how you stretch. 

Anterior pelvic tilt - lordosis of the lower back
You will be tight in your quads and front half of your adductor group (inner thigh).

Posterior pelvic tilt, flat backed
You will be tight in your hamstrings and the back half of your adductor group (inner thigh)

Don't assume it's the same in both legs, they have the opposite tightness happening. :-)

Follow my instructions and slowly feel which side of your pelvis you can do those little circles with easier? Don't necessarily feel for discomfort as it can be misleading. Look at whether you can get into that position with your legs wide without your lower stomach / pubic bone being pulled downward towards the ground. If it is, reduce the width of your stance and keep trying to increase it daily. 

Move slowly, not fast.  Moving fast with only engage elasticity, moving slowly will start to change your tissue. Slow small circles, maintain the stretch throughout the circumference of the circle.