Fun fact, in Japan sometimes 0.2mg finasteride daily gets prescribed to patients, which can be increased to 1mg daily for androgenetic alopecia. They actually have 0.2mg propecia tablets over in Japan.
0.2mg daily will actually inhibit pretty much the same in terms of serum DHT levels as 1mg daily.
However, 0.2mg daily will be less effective overall as 1mg daily. This is probably due to the difference between serum and local tissue levels, as DHT exerts its biological activity in an endocrine/paracrine/autocrine way to the androgen receptor at the hair follicle.
Point being is, yes there are certainly people who can "maintain" their hair with a lower dosage than 1mg daily.