i was a landscaper for 7 years and am rainbird certified either way if you have head to head coverage, not arc to arc, then you will not have dry spots. i water my lawn twice a day every day just for an appropriate amount of time and i dont have any brown spots despite the heat. it you're using rotors i advise rainbird 3500's from cps of other irrigation supply places. for popups rainbird 1804's have always worked well for me.

edit: just straightening your heads and raising them to the proper level and cleaning around them will help tremendously