How much it's reduced (viscosity) and the tip size
are equally important. If it's to thick then you need a bigger tip.
Or you need to reduce it more.
Once you have it right you can measure the viscosity with a
viscosity cup that most paint stores sells and always reproduce
the mix. Some paints spec viscosity but mixing to the instructions
is a much safer approach. If you do that and it's still to thick
you probably need a bigger tip.
I know if I remove the air supply to my gravity gun and pull the trigger
the paint should flow out in a steady stream, that's a "quick and dirty"
verification test for me.