Do DHT Blockers, in general, reduce the level of DHT in the body as measured by a blood test, or is the intent to reduce/block DHT in the scalp? Could you have high levels in blood test results and still benefit by Avodart/Finasteride?
DHT blockers reduce the level of DHT in the blood stream/body and anywhere it has appropriate receptors. The prostate is a good example and sometimes people who are having a hard time urinating (usually over 50 years old) will find that Propecia makes the urinary symptoms better.
Hairs that are sensitive to DHT will fall out according to their genetic fate. You can have very high levels of DHT, but as long as your hair is not sensitive to DHT, Propecia will have little effect on the normal hairs.