Like Tom said, tannin extraction is about temperature and pH. You meet the temp requirement (above 170F) but normally, acidity in the grains can keep the pH below 6 where you don't have a problem. In your case, though, your steeping was at 8 qt/lb which is way high. The acidity in one pound of grain (especially a low acidity grain like C20) is probably not going to be enough the pull the pH of two gallons of water down below 6. You could have an issue.