Sorry for the intrusion, new here and all, but I found this post interesting as I have been lurking the hairloss boards around like a spider in heat.
When you are changing the hormone balance in your body you can expect to see shedding to begin with. It is actually a part of every hair growth regiment out there. It is even said that the more you shed to begin with the increased chance you'll get more growth back as the follicles are now switching phases(anagen, telogen and whatever their name is). The reason a lot of men give up on their treatments is because they get scared because of the shedding, but if they were to just persevere it might actually have worked for them.
The simplest way to describe it is that your current hair, just like your current skin(before HRT) is built up on a body that is accustomed to a different hormone. When you switch over the hair also has to switch over and to many people's fear it is more visible than the skin you shed when it starts to align itself to a different hormone in the system. Remember that hair is a slow grower so if you want to see regrowth you won't see it in a month or two unless you're one of the lucky ones. Some regrowers didn't see regrowth until they had been doing stuff for a year or so.
I might also add that there are two types of estradiol(just like there are two types of DHT) and recent research has shown that the estradiol-beta can inhibit growth while the other one encourages it.
So if you're shedding you should only worry if it continues for months to years and there is no sign of it coming back(despite your actions). In that case there might be other problems like your thyroid, insulin resistance and more, and then your best choice would be to evaluate your diet and see if you're eating something that your body is intolerant to.
This is just a general description of what is going on on the hairloss forum. There is more, but these are the major highlights.
Also, if you want to try to speed growth there is currently some word that miconazole nitrate can boost hair growth. Both men and women have reported increased growth with it, but it doesn't seem to work for everyone. Note that Miconazole Nitrate is a fungi destroyer and there is hairloss associated to fungus growth in the scalp, but usually in children.
The rule of thumb that most hair growth companies go by is that you can more or less regrow hair if it hasn't been lost for more than 10 years. If it has been lost for longer you might have to go full retard and bring out the fringe stuff like dermarollers and scalp wounding. In these cases the follicles might have gone too far up the dermis due to the body dealing with it like a foreign object. However, I would never say hair is a completely lost cause since I've seen people do amazing things with the weirdest stuff. If nothing works then there are several companies that are currently working on Phase II trials that might be an answer to everyone's bald issues(regardless of gender).
Sorry for barging in like that. I'm watching the hairloss forums too closely and when I saw I could maybe give some knowledge I decided to pitch in.