If a man is taking any form of supplemental testosterone (TRT), then his pituitary will go through a process called negative feedback resulting in the shutting down of LH. As most know, LH is a gonadotropin which is released from the pituitary with the mission to stimulate testosterone production within the testes. LH stimulation also helps maintain testicular size. Clomid is a SERM taken to stimulate the pituitary to create and release more LH when someone is suspected of having secondary hypogonadism, which is defined by a failure or deficiency in LH that results in low testosterone. Clomid will not work if there is any outside source of testosterone present in the body. The negative feedback initiated by having testosterone present will override any stimulation that clomid can provide.
Clomid cannot and will not increase LH or increase testicular size while on TRT. The only way to bypass the negative feedback within the pituitary and increase testicular suze while on TRT is by taking HCG, which is a gonadotropin similar to LH. HCG will hit the same receptors in the testes and help maintain testicular function and size.