You shouldn't have to drop your pressure as low as 5psi (unless your regulator gauge is out). 15psi should be fine. The paint is drying in mid air, it just sounds like you need to get closer and lay the paint on a little wetter. Your thinning ratio sounds pretty good too. I used to get this problem around the wing roots of aircraft and other areas where the paint can get swirled around on it's way to the model. It sounds like you have it figured out now, good luck.
Cheers....Snowy