I always let me stone come up to temp before cooking on it. I'm not sure what you mean by "grill plate", but if you are putting the stone directly on the grate then you effectively have an air gap between it and the heat source.
"Ron Rico, Boss. You can call me Captain Ron..."
The Naked Fatty!
FEC-100/BWS Party/Memphis Pro SS/PBC/LBGE X 2/SBGE/Mini BGE/Nomad Pellet-matic/Good-One Model 42/WSM X 2/Cookshack Smokette 008/Weber Performer/Saber Cast 500/Weber Gasser (RIP)/Weber Kettle X 2/Weber Smokey Joe/WGA/UDS/Coffee Roasting Gasser and a pickle
Remembering a friend