New to Rocker Arms

I know what rockers do, I know roller rockers create less friction therefore freeing horsepower. I know stronger, lighter rockers let the RPM's raise a little, but work with valvesprings, valves, and pushrods, which are a whole other thread. But What do the ratio's do? what's the equation for the ratios. Why do you get more horsepower when you replace the 1.7:1 with 1.8:1 on the LS1 motor? I'm guessing it has to do with lift. the bigger the ratio the more lift you get? I read an article about replacing the rockers in a magazine but it didn't explain how it created the horsepower. Just says it did.

Thanks ya'all

Edit: I apologize in advance, I just realized I didn't even do a search! Don't get pissed off, it's late, I'm tired.