You have to remember the longer the coolant is in the radiator, the longer it’s it’s in the block.
If you have 200 degree coolant coming out of the engine and an ambient temperature of 100 degrees you can only drop the coolant temperature maybe 20 degrees. Maybe.
There is some math to calculate all that out, but it requires me to use a scientific notation calculator and I’m not sure of all the variables. But a 20 degree drop is pretty close.
Now get the coolant coming out of the engine at 180 degrees. Because the coolant isn’t staying in the engine as long, it picks up less heat. Picking up less heat makes it easier for your 100 degree ambient temperature to get that 20 degrees out of it.
Of course, your thermostat opening point and the ability of the rest of the cooling system to do its job will determine how well the engine gets cooled.
The closer the engine runs to the thermostat opening temperature the better the cooling system is doing its job.
