The large tank should have a pressure cap on it, it was suggested to me to run an 8psi cap.
so, how the system works in my mind the smaller tank works as usually, except instead of pressurizing and blowing off into the large tank, it simply spills into the large tank as it expands.
the bottom of the large tank has suction going to the water pump.
so the when the fluid goes through the thermostat, it goes to the top of the small tank, then from the bottom of the small tank it goes to the top of the radiator ; any extra air or fluid goes to the large tank either from the small tank or from the bleed line at the top of the radiator.
from the bottom of the radiator it goes to the water pump also to the water pump (suction side) is the hose from the bottom of the larger tank.
the only problem I could see is if you don't have enough fluid, any extra fluid would blow off out of the 8psi pressure cap on the large tank.
this is how I have it set up and my understanding of the set up, I could be wrong.