Matching your arm swing with your body motion is extremely important to developing the consistency and impact positioning on a regular basis.

The body itself must get out of the way of the arm swing both in the backswing and forward swing.  If the body is not clearing the arms will crash into the sides of the body resulting in an inconsistent impact positioning.

Basically, you must allow the shoulders and hips to rotate to free space up for the arms to swing out in front of the body.  In other words, allow the body to turn during both the backswing and forward swing.