The size decrease is due to atrophy. When you take HCG, it'll increase their size because it encourages them to function again to a certain extent.
SERMs work in a similar way by stimulating LH release, rather than using HCG that acts as a mimic to LH.
It just doesn't work that way. When you chose to blast and cruise, you gave up the option for a normally functioning endocrine system with regard to testosterone, LH, FSH, sperm count, as well as a number of other hormones and hormonal processes. That's why it's a big decision, a life choice that should only be made when you need it due to a lack of natural testosterone. You can't have your cake and eat it too... You can take HCG and maintain some function but it's limited, it's mainly so that if you do decide to get your natural system operating again it'll be easier. Instead of letting the car sit for a long time and the battery going dead, you can keep it on a trickle charge so it'll hopefully be ready when you turn the ignition...