I ALWAYS use a drop of water and a drop of medium/transparent base in my paint. Then a drop of paint if I want transparent and 2 drops if I want opaque. A quick spray at 2 bar and see how it covers. Too opaque, I use medium. Too transparent I use paint. Try again until I get close. Then it's time to work on flow. I turn Mac valve shut and pull back trigger till where I want to see paint start spraying. I slowly start to open the Mac valve until it starts spraying. When pressure gets too high for my liking, I start adding water. This does change opacity too, but coverage at low pressure gets better the closer you are to the surface anyway. So I shut valve again and start again. If paint gets too transparent I know I have to settle for more pressure. So I then add a drop of paint again. So I basically adjust the paint to match the low pressure and only when I've "broken" the paint will I up the pressure. Back and forth like this and I get it in about 30 seconds of trying.