Or make a good, experty tended, three stone fire. But, the pot is a terrible heat exchanger. So only a small percentage of heat actually gets into the water and food. The percent of heat that makes it into the food can be increased by exposing more of the pot surface area to hot flue gases, optimizing heat absorption at the pot surface, using multiple pots, etc. For example, the bigger the pot, the greater the heat transfer efficiency.
Full pots score better than half full pots.
A skirt around the pot dramatically improves efficiency. Covered pots save fuel. Professor Grover ends his report by including a paragraph on pot design. I heartily agree with him that a new pot, designed to increase surface area to volume ratio, and that forces heat to rub against the pot surface would dramatically improve fuel economy. Effort spent in improving the pot as heat exchanger is many times more likely to improve cooking stove efficiency than improving the combustion side of the equation.