It's the nature of the beast, rather sucks. Essentially what is happening under normal circumstances is, we have a part of our liver that controls our Iron levels, it's referred to as Hepcidin.
Testosterone is known to suppress Hepcidin therefore increasing Iron uptake in blood, hence the elevation of Hemoglobin. It seems that as we age the use of Exogenous Testosterone further suppress Hepcidin more so than in younger aged males, unless they (younger males) are predisposed to hereditary Hemochromatosis, in which this is believed to be a congenital defect with Hepcidin regulation.
Another possibility that those on TRT tend to ignore is OSA, sleep apnea is common place for increased Testosterone levels. In the presence of sleep apnea, Hypoxic hypoxia is a result of insufficient oxygen available to the lungs during sleep hours, when this happens our body sends a signal to our bone marrow to increase Red Blood Cell production.
So with all that said, there's possibly a few other causes that's raising your HH, ie; Iron intake or some other underlying cause such as heart and lung diseases, smoking, dehydration ect, ect.
Some feel that cardio helps lower HH, for me, not so much, as I've run anywhere from 3-4 miles every morning. What helped me from having monthly phlebotomies was being diagnosed with OSA and wearing my CPAP religiously every night.