Mark,
The Fibrament stone sits on the metal pan (on an air pocket)that deflects heat to the outside of the stone and to the top stone.
If there is not enough heat there will be little or none that gets deflected so the bottom would burn since there is a lack of parity between the top and bottom stones. The Fibrament stones are heavy and hold a lot of heat, so they don't cool down that much when the cold dough comes in contact with them.
The stone will not reach optimum performance levels untill it's been fired up 10-15 times.
Willard