If DHT is responsible for hair loss and Propecia blocks it I don’t see why it wouldn’t work for the front. Yes, regrowth it may be useless but halting the front from thinning it may work just as good as in the crown.
It does occasionally work in the front. One of my sons had a great impact with the return of much of his frontal hairline while on Propecia. When we report that it may not work in the front, it is because statistically we see much better results in the top and crown. It is just the way things are! We can also ponder why hair loss in men affects the crown and the front in the classic “male pattern”.
While DHT is a factor in genetic male pattern baldness, it is not the only factor. There are still many factors not yet discovered. We still do not know why DHT only affects the crown area in some patients.