in a newly rebuilt A15 engine with a new 3 core radiator running an electric fan & a re-cored heater core & new control valve my temp gauge is always at the middle of the gauge or slightly under it. Laser temp says its 178 - 180ish F water temp.

you can see the gauge a little.....



Likely its not just airflow, if any of the cooling system components are original or have a lot of age to them it can be all factors. Blocks, radiators, heater cores & valves clog & reduce flow - most likely candidate is the radiator water flow .

Getting hotter at idle should be more common as theres no airflow over the rad as well as less coolant circulation thru the motor.