Look at it this way Roger---we're talking about the fan control--we're varying the amount of air flow thru the radiator --its the only variable that we have any control over--the thermostat will have the coolant coming out of the engine at 195 no matter which of the 3 holes you put your sensors in or even if you don't use any. You need to run the fan only if there isn't enough airflow thru the radiator to cool the liquid down enough to keep the engine under control of the thermostat--the key element here is the temp of the fluid leaving the radiator---so put the sensor at the outlet of the radiator and thru trial and error determine what the temp needs to be---set the controls so the fan comes on as the temp gets up to that temp and shuts off as it falls below that temp

If you care to really get a feel for what is best for power / economy, check the temps in and out of the raiator to find out how much the radiator will drop the temp and then adjust the sensors/thermostats, etc around that data.