You can increase the media flow rate up to some limit. You will have to increase your air pressure as you increase media flow rate in order to maintain your intensity. Eventually the media flow rate will exceed the nozzle capacity (or air pressure available to maintain intensity). You could also consider using a larger diameter nozzle (and your compressed air consumption will go up dramatically). If you go to larger nozzle consider also going to larger blast hose.
Perhaps you can increase the number of nozzles.
Another was to increase coverage rate is to use smaller media (if allowed). You would maintain constant media flow rate pounds per minute but each pound of the smaller media has more particles (also known as dent makers...) and therefore your rate of coverage goes up quickly. Hope some of this helps. Let me know your progress.
