I've had success with 3mg/week of EC as monotherapy for well over a year. It all depends on your body

Nvm. Per https://transfemscience.org/articles/injectable-e2-meta-analysis/

Additionally, it was noted in this meta-analysis—based on clinical research in cisgender men with prostate cancer—that only modestly supraphysiological estradiol levels, of no more than approximately 200 to 300 pg/mL, are likely to be needed for strong testosterone suppression in transfeminine people. This has likewise been confirmed with solid clinical data in transfeminine people by Herndon et al. (2023), with 88% of those on injectable estradiol monotherapy having testosterone levels of <50 ng/dL at a median injectable estradiol dose of 4 mg/week and with median estradiol levels of 220 pg/mL. It is the opinion of the present author that Herndon et al. (2023) is a very important and formative study, with clinical implications that go far beyond merely supporting the s.c. use of injectable estradiol. The study represents the first major step in the published literature to correcting the dosing and intervals of injectable estradiol in transgender care guidelines and in transgender health generally. I commend the researchers for their work.