I have different ideas from some of the experts here. I have a try Green background, also. I believe in waving the gun back and forth, covering a swath of about 7 feet. For that you need a nozzle that puts out a circular pattern. (Raindrop nozzles at try Green, but you may need to go on a lower volume).
Remember if you use a flat fan nozzle--or any fan nozzle--you hand must remain stationary at the same height and angle, as you walk forward--moving it left or right causes huge uneveness in application. In fact, even a slight up or down movement of your hand as you step forward will cause major variations in the pattern on concrete.