It's caused by a poor progesterone:estrogen ratio. This isn't something that can be assessed using serum estradiol, as estradiol is not an endocrine, but a paracrine hormone. This means that is is produced and used in it's tissue of origin, meaning serum values are largely useless.
Jefcoate, C.R., et al. Plasma Estrogen Does Not Reflect Tissue Concentration of Estrogen. J Natl Cancer Inst Monogr. 2000;(27):95-112.
"However, breast cancer tissue E2 levels are 10-fold to 50-fold higher in postmenopausal women than predicted from plasma levels. Consequently, factors must be present to alter breast tissue E2 levels independently of plasma concentrations"
Akerlund, M. et al. Comparison of plasma and myometrial tissue concentrations of estradiol-17 beta and progesterone in nonpregnant women. Contraception. 1981 Apr;23(4):447-55.
"The tissue/plasma ratio of E2 ranged from 1.45 to 20.36 with very high values in early follicular phase and the lowest in mid-luteal phase"
Batra, S., et al. Interrelations between plasma and tissue concentrations of 17 beta-oestradiol and progesterone during human pregnancy. Clin Endocrinol (Oxf). 1979 Dec;11(6):603-10.
"The general conclusion to be drawn from the present study is the lack of correspondence between the plasma concentrations and the tissue concentrations of female sex steroids during pregnancy."
I understand these studies are in women, but the general concept of serum estradiol being a poor representation of tissue concentrations is just as applicable to men. Perhaps even more so, as we rely almost solely on peripheral conversion since we don't have ovaries.
Get your progesterone tested. HPTA shutdown causes impaired choesterol -> preg conversion, and thus low progesterone, whilst simultaneously increasing systemic estrogen due to large amounts of exogenous testosterone. The end product is impaired progesterone and raised estrogenic activity, which downregluates the overall metabolic rate of the cell, thus causing edema - a manifestation seen in all stressed tissues. No amount of estrogen control, dht, ai, or diuretics will fix it if your prog is low from hpta shutdown. Progesterone's regulatory role over aldosterone which is lost if it becomes deficient also plays a big role too.
Anecdotally, I had insane water retention on TRT, and my progesterone always came back at undetectable levels of < 0.14 nmol/L. The retention melts away everytime I come off, and my progesterone levels sit ~1.2 nmol/L.