Fling, i could be wrong, but I think that your thinking about it as a static system instead of a dynamic system.
When the blades are flapping they are essentially scribing a sine wave if you drew the tip path on a peice of paper.
So assuming that the helo is at constant speed, and no input forces are being applied to the blades each blade will hit the same point at the same position. This will change when there is an disturbance to the system as a whole, then it will flap to equality, balancing the system out.