If you raed what I posted I said I keep it about 3 feet from the surface. I am using mostly the wind force created by the high pressure to blow off the soap. We hand wash the cars and between the 2 of us we can get a car done in about 2 minutes.That is soaping, hand washing the whole car, soft water rinse to get the soap off and then following with a spot free rinse, then towel drying them as needed(even DI water will have some spots if the soap dries in the sun). DI water cost me about 5 cents a gallon. So that is why I use a seperate gun for DI water. I would use all DI water but then I would waste a lot of DI water just clearing the line all the time. I use one gun for the soap and soft water and another for DI water. Depending on how it goes I sometime just DI rinse the whole car if I get to close to the guy mitting the cars. I just raised my prices and I know get between $2.75 and $3.25 a car. That is why I hand wash. On good days the 2 of us do about 26 to 30 an hour. When things go slow we still do 20 to 22 an hour. I usually make no less then $65 an hour. Not the greatest but it is steady work. Not so much this year though with the heavy rain we have had in my area. Doings cars is all about volume and speed.
Sorry if I got carries away. I assuming you are just washing your own truck at home right? We are setup to do many cars in a short period of time. Just remember that 3000 psi is rated at the impact one inch form the surface being cleaned. For every inch you back away the impact force lessens. With 3000 psi I can spray your hand at 3 feet. Just not with a zero tip.LOL.