Some doctors are recommending using 200–500 IUs twice a week for men who are concerned about testicular size or who want to preserve fertility while on testosterone replacement. Higher doses, such as 1,000–5,000 IUs twice a week, have been used but I believe that these higher doses could cause more estrogen and DHT-related side effects, and possibly desensitize the testicles for HCG in the long term. Some doctors check estradiol levels a month after this protocol is started to determine whether the use of the estrogen receptor modulators tamoxifen (brand name: Nolvadex) or anaztrozole (brand name: Arimidex), is needed to counteract any increases in estradiol levels. High estradiol can cause breast enlargement and water retention in men but it is important at the right blood levels to maintain bone and brain health.
A very well known doctor in the field of testosterone replacement, Dr. John Crisler (allthingsmale), recommends 250 IU of HCG twice per week for all TRT patients, taken the day of, along with the day before, the weekly testosterone cypionate injection. After looking at countless lab printouts, listening to subjective reports from patients, and learning more about HCG, he reports to be shifting that regimen forward one day. In other words, his patients who inject testosterone cypionate now take their HCG at 250 IU two days before, as well as the day immediately previous to, their weekly intramuscular shot. All administer their HCG subcutaneously, and dosage may be adjusted as necessary (he reports that rarely more than 350 IU twice weekly dose is required).
Hope this helps. In theory you should get a test boost, and a natural scrotum position (versus drawn up) as HCG mimics LH which stimulates the leydig cells to produce Test.
I am guessing in you probably know all this...