I am building an aluminum melting furnace. I have the burner done but I don't seem to be able to find where the best placement of the burner should be. I plan to have a refractory poured floor with a drain hole in the bottom. The hole will be covered with a refractory disc which will hold the crucible. How high above the disc should the burner be placed? Should it be placed at the bottom of the crucible? Thanks for any help.