You need to give the body time to multiply leydig cells before stimulating them or you will just desensitize the receptors. Sure many people can stay on TRT while doing fertility treatments, but that is because they still have enough leydig cells left to begin with.
Can you explain where you're getting this from? I don't mean to be argumentative, it just gets so frustrating hearing so many different things and spending so much time and money so far with no results. I've heard from Dr. Crisler, Dr. McClain, and Dr. O'Connor that leydig cell desensitization is a total myth and there's no proof of it. I've read dozens of studies now on HCG, HCG+FSH, and clomid for fertility and have come across nothing regarding leydig cell desensitization. Everything I've come across has shown superior results with higher doses, and I've never once heard a protocol suggesting one needs to come off for a long period of time before starting HCG and FSH nor have I seen any evidence of this.
I have heard of people saying that for those who want to restart it can be beneficial to do a few weeks of HCG to stimulate the leydig cells, then do clomid to restart the pituitary, but that's an entirely separate issue.