Smaller roasts take more hours per pound than the larger ones. Yours took about 3.5 hours per pound, which is typical for the smaller sizes. You can think of it this way, it just takes a certain amount of time for the collagen and connective tissue to convert to gelatin and get tender, no matter what the size. So no matter how small, there is a minimum amount of time it takes to make that process happen. 12 hours might be pretty close to the minimum. So as a recommendation in general, allow at least 12 hours minimum for any size, then the larger the roast, the closer to 1.5 to 2 hours per pound you will get.