Some clarifications on this: The estradiol
is a result of aromatase—"Leydig cells have a high capacity for aromatization and ... hCG can acutely stimulate aromatization independently of stimulating testosterone synthesis in vitro."[
1] The reason this estradiol production is resistant to AIs is due to the high concentration of intratesticular testosterone relative to serum levels, ~40 times greater.[
2] My assumption is that it's not practical to make intratesticular AI concentrations high enough to counteract this.