I have to agree with the other guys, in my experience MM can be really thinned, I also go as high as 1:1 if needed.
Colder air indeed does not aid paint application with an airbrush, the flow, the spray pattern and the risk of runs due to slower set up are problems that can be encountered.
Some say higher pressure can assist in reduction of spatter at edges. Seems like my better fine line results are to be had at 18-25 psi.