here's my 2 cents...and i've been wrong before.
The thermostat sets the maximum temperature and starts to open when that temperature is reached.The temperature will continue to rise about 5 or 10 degrees until coolant from the rad lowers the temperature in the heads and cylinders.The thermostat never fully closes after the initial opening and the temperature will not change from then on.The speed of the coolant must be reduced to a level that keeps it in the rad long enough for the heat to be dissipated by the rad, usually about 30 degrees (Delta T) If your cooling system is not adequate the temperature will rise when conditions become more severe like a stop and go traffic.
The heat exchanger or rad and fan are the only items cooling the engine temperature if all else is working correctly
Monkey around changing flow ,thermostat or other components is like throwing darts and you may end up with a system that works great or a whole pile of grief!