When microwave cooking, the amount, size and shape, starting temperature, composition, and density of the food affect cooking results. Size and Shape: Smaller pieces of food will cook more quickly tha...When microwave cooking, the amount, size and shape, starting temperature, composition, and density of the food affect cooking results. Size and Shape: Smaller pieces of food will cook more quickly than larger pieces, and uniformly shaped foods cook more evenly than irregularly shaped food. If cooking several items of the same size and shape, place them in a ring pattern, leaving the center of the ring empty.