ways to increase manpower production beyond level 3 recruiting centers

I have level 3 recruiting centers in all of my core cities and have even started adding them to surrounding provinces. In day 6 and still only producing about 821 units per hour. I checked another player with espionage, and he has 18k worth of manpower. This is the one area I am constantly behind in. I have 82 Units built. 1 troop loss and 131 kills.