I don't fly choppers, so I can't say.
If the string is just a wool string like those of sailplanes, the string will be offset, too, because there is a slip angle, the air doesn't come from dead ahead. It should be on the opposite side of the ball, I think. yawing right with wings level, the ball would move to the left by centrifugal force and the string would be floating to the right because relative wind comes from the left.