Every thing comes back to the thrust angle.
To do a radar calibration the thrust must be at zero.
I know how the system works and regularly drive them,
I would not want to be doing 70mph racing up behind a car that's braking hard relying on my Active Cruise control to maintain a good distance from the car in front, when it cant see it because the calibration is out.

If anyone doesn't understand why its important to calibrate these properly please read up on these systems.