An SHBG sponge analogy is compatible with your other points. I've used a similar reservoir analogy. Think of testosterone as like water being dripped onto the sponge. The important feature is that the sponge saturates, at which point it doesn't interfere with the "flow" of free testosterone—free testosterone being driven exclusively by endogenous production or exogenous dosing. If you double the size of the sponge then the flow is temporarily impaired until the sponge is again saturated. Then free testosterone flows the same as before. A larger sponge means more total testosterone is held, but at steady state this is independent of the flow of free testosterone.The idea of SHBG as a sponge that sucks up large amounts of testosterone and leaves your free T low doesn't seem to be how it really works. The way I understand it, high SHBG makes your meager production (revealed by the free T) look like it's normal or even high when it isn't. The SHBG is basically extending the half-life of the testosterone you've produced and the relationship seems to me alot like ferritin and iron.