I never have to turn pressure down or switch lances or anything else , use the same pressure adjust the spray angle away from the area you do not want to disturb.
The ball valve can be bad on the pump and the unloader as well creating too much back pressure, it is ok at a low pressure but I prefer not to use it that way.
The pumps on a pressure washer are designed to work at a certain minimum gpm restricting the flow in my oponion is not good for the unit.
As far as the way we do it ? Well it takes some getting used too, Ash has seen the way I do it and can vouch for our methods and changing tips wands and lances takes time as well
Basically if you can stand in the bed you are ok, spray away from it if not hold the wand away from you and spray back toward your feet