Because % of body fat has a lot to do with how some agents can stay in the system. In addition, it should be noted that the body weight of a HW requires higher doses of the agent (like any other medicine) to receive the same benefit as a smaller fighter. A buck and a quarter flyweight's liver & kidneys are not that much different from a 250 pound man's! Certainly not nearly 2X.
FFS, Mighty Mouse could "potentially" be a kidney doner to Lesnar!!!
1 MG of substance X could do wonders for a 125 pounder, and be cycled very quickly. The 2 MG of substance X to give the HW the same bang for the buck takes damn near 2x to clear, and that is one of the leanest HW's I am talking about.
I would imagine PED's could find a permanent home and be tested forever in Hunts blubber!