How does the Dr. exactly know at which Line the DHT immune Hairs begin? Does he just take Hair from the lower back of the head to be sure those are the 'good' Hairs?
The "Safe Zone" with DHT resistant hair follicles is the zone that runs approximately from ear to ear.
However, a lot of FUE surgeons these days extract hair waaay outside the safe zone. Those hairs are not DHT resistant and the patient will likely suffer further hair loss unless he is taking meds.