Fascinating. You were on Testosterone, an aromatase inhibitor, your DHT was double normal, and you still had sparse facial hair.
So what other chemicals/messengers come into play here?
Within ghostwritten articles about "why some men can't grow facial hair," the implication is that the genetic distribution of DHT receptors is somehow lessened in these men. They go on to say that these men have a low risk of losing hair, but this is clearly bullshit. I have typical male pattern androgenetic alopecia and a rather regular distribution of chest hair.
However, we could assume that the DHT receptor deficiency is limited somehow to only these specific hair follicles. It's certainly possible, as the hair around the edges of most males scalp
is also fully DHT agnostic, which is why successfully transplanted hair sticks around for a lifetime and why men typically lose hair only on the top of their head and not the sides.
Then again, if the follicles aren't receptive to DHT, why do I have any facial hair at all? Why would it come in sparsely when, normally, DHT sensitivity is localized to an area of hair follicles uniformly; not speckled randomly to, say, every Nth hair follicle.
My particular hormonal anomaly is a deficiency of SHBG. Women with PCOS also have an SHBG deficiency along with their high androgens. Delivery of DHT to tissue and/or activation of the DHT signaling pathway (via contribution from SHBG-R, the cellular SHBG receptor) could come into play.
Here's a horrifying image of what a PCOS beard looks like. Her androgens are high, but only the bottom of her face grows hair: