Chicken Count in AA?

I'm in AA grade and I consistently use 5 10x Prisms for 4 hours. I generally get around 300 million chickens without much effort but 1 billion tends to be more of a challenge. Whenever I finally get a 1000x Prism, I almost always use it out of panic that my contract won't finish. Does anyone have any other tips for getting more chickens consistently or what to do otherwise?