...and besides that: as soon as the system is too low on refrigerant the airco wouldn't even start getting cold anymore. As soon as the airco is activated you get a constant low temperature that gets mixed with air from the outside.
Setting a lower temperature means less air from outside, setting a higher temperature means more air from outside; the vented air inside the car is a mixture.
A lower temperature setting does not mean that the airco gets colder; the temperature that is generated by the airco is constant...
with a minor 600+k