Well everyone is different. Some people don't lose much hair, some people bald prematurely and lose lots of hair early on. Reducing your testosterone levels will almost certainly help with your hair line, but results are different for everyone I'd imagine.
For me, on my 7th month of HRT, I have noticed a substantial difference in the overall volume of my hair. For the sides of my bangs, where most men would start to lose their hair first, it's started to grow back in, Granted I didn't lose much, because I am still young (25).
It is also growing back just above my sideburns, more into the middle of my forehead.