Why do I need more time and liquid than my risotto recipe calls for?
It doesn't sound like you're doing anything wrong. I've found risotto to be one of those recipes that can vary up to 50% (usually less) from what the author calls for and still turn out great. I've even used recipes that call for "2-4" cups of broth. You may be overcooking it though, the rice should be al dente. It's not uncommon for people to overcook this until you have a mushy risotto.