I don't think that's likely. The upregulation probably occurs everywhere prolactin is active but is only evident in tissues that express 5AR (DHT conversion doesn't require high T) due to Testosterone being lower.
Hm I wasn't hinting at environment being more important than genetics. Supraphysiologic are doses of a substance that are FAR larger than would ever occur naturally. This type of environment, with supraphysiologic levels of DHT, would never occur naturally in any population and would have to be artificially induced. The degrees of resistance that different people's hair follicles have to DHT is entirely genetic and some people are so resistant that we effectively consider them immune (i.e. they won't bald in their natural lifespan).
If human lifespans were extended to multiple centuries and Androgenetic Alopecia was not cured/treated(cruel world if this ever happened), it would be interesting to see how immune the people who we consider immune today are.