Gullibell
In your 10m example your 10 m line will still hit the tail rotor ! Unless I am mistaken the length of a helicopter would be nose to the last point of airframe. Now forgive me but in all the types I fly ( with the exception of those with either a Notar or Fenestron )the tail rotor blades have at least 50% of the turning circle within the total length of the helicopter.
It is much more critical to measure the distance between hook and tip path plane of the tail rotor