On the grill, the entire body of MPO is exposed more or less to the same amount of heat. Even when I tested MPO on the gas stove top using all 4 burners, no problem, all 4 corners were exposed to heat (but there too much heat than the MPO vent can flow out, so there was too much heat comming from under MPO and getting my stove really hot.
But with only two burners, the heat from the burners was concentrated at the bak of the oven, which heated the back to a temperature much higher than the front. Which caused MPO back roof to flex down. Due to the temperature diference between the back and the front, Turning the pizza while baking is not enough in this cas, a turning stone mechanism is essential for baking to get even temperature all across the bottom stone and getting pizza exposed to the MPO back high temperature equqlly.
plus, the plate prevented some of the heat to escape when MPO is closed.
At least, that what I think happen.