Yes, cover plates are designed for that very thing. After you cover the first one, see how it goes. If you cover part of the second concave as well, you can start to slow the rotor down a little to help eliminate cracked kernels. If the cover plates still are'nt enough for what you wish to see in the tank, try cutting about 4" lower if you can, to use the straw to help rub the grain out. Also, make sure you keep the machine full and have a consistent load of material.