Hi farbanian,
I can share my experience with oral estradiol -- but with the understanding that people react to hormones very differently.
My endo has worked with transgender folks for decades. He seems to be very highly regarded within the local transgender community. I started HRT last August, about 10 months ago, on a very low dose -- Spiro and Estradiol, orally. After three months I had my blood drawn and a checkup. Blood draw showed testosterone levels very low and estrogen at 95. At the time I had my blood drawn it had been a little over 24 hours since my last estradiol tablet.
My endo said the he likes to see estrogen in the 100-200 range for full-on transition. He said that my 95 on a low dose was nearly there. Still, it was such a low dose that he doubled it. My estrogen level at the next blood draw about 3 months later was about 240-something. He has maintained that dosage since.
At work I drink about 80-100 oz/day (roughly 2-3 liters). Not quite the same as your 4l, but still a lot of water.
I had asked about injectables and bio-identical progesterone at my first appointment. He wanted my to try the estradiol first, and discuss alternatives after six months. At a nine month check-up I asked again about progesterone. He said let's do that at the two-year mark. Clearly, he has his own opinions on what to do. I can't really argue that his approach isn't working , because it is working for me. I would like results to come faster, but that's not the way HRT works.
So, keep talking with your doctor. If you don't think your doctor has enough experience with HRT and transgender folks, then look for a different doctor. If you think he has good experience, and seems to really want to help, then try what he says for a while.
Kim