The general function of a heat exchanger is to transfer heat from one fluid to another.
Again, the laws/formulas that dictate the thermal capacity of a heat exchanger are known and available in your basic thermodynamics classroom book. In non of them does dwell time reverse the formulas outcome. Further more in no case will increasing the flow of heated fluid (decreasing its dwell time) reduce the total thermal transfer of heat energy. The system will eventually bottom out and not improve, but it will not start going the other way. You will only thermally saturate the cooling fluid to the point that it can no longer absorb anymore heat.
Example below:
You have two radiators with all variables the same with the exception of the volume/velocity of heated fluid flowing through the core, one is 50% the other is 100% of the systems capacity. In the 50% low example, the mean coolant temperature across the core is 150* the other 100% example is
example the mean coolant temperature is 195*. Which example will transfer more heat energy out of the system? The 100% flow example because the mean Delta T is greater between the two fluids is greater.
Sorry to preach but these are basic system fundamentals, and I'm fine if we agree to disagree, this won't change my initial question. Off to work and then out to the garage.