In my mind for a street vehicle if everything is sized right the thermostat will modulate to control to a fixed temperature - with a 195F stat you will run 195F once up to temperature, and it will not vary from 195F unless you lose air flow, your radiator is too small or your water pump drops flow. I like the idea of putting the fan control sensor at the exit of the engine or inlet to the radiator, telling you that the fluid is going to need additional cooling (feed forward control). If you put it on the cooled side (feed back control) then your temp is going swing before you take any action, and if the fan is sized right you will over correct, cooling more than ideal. With feed back control and any component undersized (or low speed operation, low air flow) your operating temp will tend to swing up and down on some form of sine wave. Feed forward will be more stable for the street - just my $0.02.