ime I've run into problems by varying too much the amount of fuel I use. The size of the cooker and the space to be heated dictates to some degree how low you can go on fuel and still achieve and maintain the desired temp for the necessary time. If you're using MM for a short cook you can probably get by with 3/4 chamber full and 20 or so lit. With Standard, I would stick with one lit covered by one unlit.
Paul