Hunters current nozzles for the PGP and I20 rotors offer good distribution. If they are older nozzles and can be replaced with new ones do so. Is the pressure at the head sufficent for good dispersion?
Going with larger nozzles may be a no-no because the water source, main & lateral lines and valves may not be designed for greater flow.
How about jsut running the sprinklers longer? You may not be putting out enough water per week to match the evapotranspiration rate of the turf.