Yeah, I'm going to try increasing the pressure a little as well as I'm not getting the desired range and the paint does seem to be coming out a little weaker than I was expecting.
Thanks for the help Gee Tee, hopefully I can now save myself money as I'm not having to recoat the fence so often and now my fence too can look a deep, strong "forest green" rather than the weak pathetic "mint green" that it previously wore.