I use a finishline III gun and when I first got it I had a problem with orange peel. I've found that it likes more pressure. I usually do 23-25 inlet psi and it'll lay down smooth. It may be rated for hvlp at 23 psi, but I'm not convinced that's it's ideal pressure in the real world. Bump it up just a bit and see what happens. My 0.02.
81 Grand Prix, 355, 700r4, 8.5" 4.10
64 Oldsmobile Jetstar, all original