That doesn't make much sense. It's up to the market to price the shares, which will determine their yield percentage. Targeting a particular rate of yield is not something FC can control unless he can set the share price.
In general, yield will be high when there is not much expected future growth. Yield will be low when the market is expecting future growth in dividends.
Look up when exactly FC wrote that and think that he intended to maintain divs at 5-15% a year.
You can look for it all you want, but I don't think you're going to find it. Like niniyo said, the market controls the share price and the resulting dividend yield.
That post shouldn't be too hard to find if it exists. It's not like he posts 10 times a day.