The pressure setting is determined by the type of paint and thinning ratio that you use. I normally paint with Scalecoat II thinned at 50% and set the pressure from 20 to 25 psi. For weathering, the thinning ratio is closer to 75%, and I increase the pressure to around 35 psi because I like the "dusty" effect I get. I usually spray (thinned) acrylics at 10 to 15 psi. I haven't used Floquil, so I don't know what pressure to start with for their paints. Generally, start with the manufacturers' recommendations, then experiment till you get the results you like. You can paint (and re-paint and re-paint ...) an old shell or use scrap styrene for practice.