The bro science on this is mostly wrong.
The ideal level of e2 for maximizing IGF is approx 15-35.
Much below 10, or above 35, and liver GH resistance increases.
The reason some equate high e2 with high IGF is because high e2 stimulates higher GH secretion, which still increases IGF despite higher GH resistance pushing IGF conversion efficiency down.
But that's endogenous GH. If all your GH is exogenous, and high (or extremely low) e2 is blunting conversion to IGF because it causes GH resistance, IGF will go down as e2 goes up, for the same rHGH dose.