Using an HVLP gun with the cup on top...for small stuff, but it needs to be able to lay a smooth surface when I spray clearcoat. Right now, it's looking like I'm spraying over something covered with sand. First off, what is the vertical knob on the bottom of the handle, by the air inlet for? Second, what does the knob straight back from the nozzle do? While I'm sure one of these lets more paint come out (or not), they don't seem to DO anything on mine. I DID find the spray pattern knob... Question: if you gun was spraying out a rough layer, what would you do to smooth it out? Thanks!