Aren't you assuming the attack is based upon sustenance? I'm thinking it's more about territory and protection of that territory. Hadn't even considered the aspect of food.
Sorry, I was out in Yellowstone recently, and the Park Rangers were talking about Bears and Wolves and that is what I was thinking of. They only go after the animals if they consumed a human or if the animal went after humans because it saw them as a food source. Incidental attacks are different. If its just a wrong place wrong time (for example a human comes between a mother and her cubs), they leave the animal alone, because its just doing what comes natural. But if they feel that the Bears start equating humans with food, they always go after it because they learned in the past thats a big problem.
One of the interesting things they discussed is how the number of Bear attacks in Yellowstone dropped dramatically once they strictly forbid humans from feeding the bears. Encroaching on their territory was less of an issue than leaving one's garbage can open. Once the Bears stopped seeing humans as a easy food source, they started going after more natural food sources, ie elk, deer, fish etc... If you get caught feeding a animal in Yellowstone, you get a $2000 fine. And if an animal is looking for food from humans, the animal gets put down.