I doubt the op had a 100 ft high mountain in the backyard he was working with. Realistically, probably a 30' rise at most whereas .06 of lb pressure isn't going to amount to didley squat. NOW if he was building a water tank in his client's back yard he just might need your expertise! Rule of thumb is still off by .03 psi. Cool job we are working on. I need to get a pic of all 91 heads in this sections running at once.