I originally was taking sublingual pills for the first 6 months I was on E. I had also worked up to 6mg/day for the latter 3 months. While everything started out great (clearer skin, hair growth, etc), I started to have some autoimmune issues. After visiting a specialist, I was diagnosed with limited scleroderma and prescribed methotrexate, a heavy duty chemotherapy drug with hairloss as a common side effect. Definitely not something I wanted to have to take long term. Also I knew the diagnosis was too much of a coincidence to not have something do to with my hrt regimen.
I found some studies that linked estrone to autoimmune problems. I also read a lot of documentation of HRT methods by Dr. Powers (an endocrinologist who is considered almost a modern medical pioneer on trans reddits). Anyway, he cited that about a third of his patients on sublingual pills had problems with massively elevated estrone levels, which was solved by switching to injections. So I had my estrone levels checked and sure enough they were about a 10/1 ratio vs my estradiol levels (1300pm/ml vs 130pg/ml), when realistically they should about a 1:1 ratio.
Switching to injections completely solved the problem with my abnormal levels and, I believe, the scleroderma issue since I haven't seen any progression despite getting off methotrexate (which had destroyed much of my initial hair growth).
Anyway, for anyone not getting any progress on pills, I suggest checking your estrone levels as well since that can impede the effectiveness that estradiol has for hair.