I have a swg now in my pool/spa so I have no experience with bleach other than using it as a shock in my old (pre pool) portable bromine spa. It just seems to reason that to raise the FC to a higher level it will require more bleach. You are probably right about not needed more to keep it there since at higher CYA levels more of the chlorine is 'stablized' and the amount of available chlorine that gets eaten up by the chlorine demand would stay pretty much the same. Makes sense when you think about it and your empirical evidence back it up!
Ben or anyone else who REALLY knows what's going on with this care to enlighten the masses?