Ok, let's say your natural test is 100mg per week (i don't buy 200mg, maybe if you're 16 with high test levels).
And for arguments sake let's say your conversion for test to DHT is 20%.
So for 100mg of T you'll produce 20mg of DHT - where your hair is today.
Now if you take 5mg finasteride (which decreases scalp DHT by 41%) with 200mg of test you're DHT will be
40 X 0.59 = 23.6 - only a slight increase in hair loss.
If you take 0.5mg of dutasteride (which decreases scalp DHT by 41%) with 200mg of test, you're DHT will be
40 X 0.49 = 19.6 - so no hair loss.
Now if you take 2.5mg of duatasteride (which decreases scalp DHT by 79%) with 500mg of test you're DHT will be 100 x 0.21 = 21 - so basically no hair loss.
What do you think ?