Fin dosage needs as relative to hairloss progression?

Im 21 with frontal thinning in typical MPB areas, also potentially thinning at the back. I can cover it up OK with nanofibers and aquamatch FOR NOW.
I am also using 15% minox and scalproller 1X per day as well as 5% regaine in the mornings.

My question is this: For a guy who has only relatively recently started the balding process do I really need a full effectiveness dose of Fin (lowering DHT by up to 70%). That is why should I not take an amount that is relative to my hairloss.

Hair loss as I understand it is caused by an increase in the binding of testosterone to 5-alpha-reductase causing DHT. Obviously for me relatively recently the frequency of this binding has increased, increasing my DHT levels and subsequently my hairloss. So why should I not take an amount of Finasteride that is relative to my small DHT increase? Like say, .1 mg would probably have half the effectiveness of .2 mg (which is the minimum effective dose) and it would probably take my DHT back to levels that they were at before I started balding, or even less. I just dont see why I guy with only moderate balding should need to take a full dose of fin.

I haven't seen this topic addressed in anything I've read so far so would be great to get some feedback.

Btw I have tried fin at 1mg and got all the typical sides but didnt stay on it long enough to see physical difference, though I know it was having an effect from the sides. So I am trying to formulate a way of reducing my intake while still maintaining my hair.