In my experience orange peel comes from not getting enough finish laid down, and the thin coat flashes off before it has a chance to flow out. A heavy coat causes runs, not orange peel. Its a pretty fine line between the two, but a run is easier to level out than orange peel. I always strain my finishes before they go into the gun, I have never used the strainer in the cup.
I can get nitro to lay down ok if I mix it 4-2-1, lacquer-thinner-retarder. The retarder is necessary because its a hot mixture with that much thinner, it dries to quick. I still get better results with my non HVLP gun, so I never use it.
I am going to have to buy another gun because I sprayed metallics, and no matter how much I clean it, I cant get all of the flake out of it. So that gun is going to be used only for metallics and primer from now on.