The reason for putting the switch on the cold side is that the thermostat controls the temperature of the water ,not the fan. The fan is only there for when the airflow is not sufficient enough to cool the water in the radiator.
So if you measure at the cold side and the water is hot ....the switch then tells the fans that there is not enough airflow and the fans need to switch on and take over and create the airflow. Then as soon as the water coming out the radiator has cooled the fans switch off!!!!
If the switch is on the hottest point of the engine the fan will run all the time..........WRONG!!!!.
The cooling system seems to be the most confusing to people..
Also remember that operating temps of 110 are not dangerous and in fact the thermal efficiency of the motor is better the hotter it is.
John
Buy a Jacket!!............................and a cap!