It's not useless at lower temps but it sort of defeats the original idea of the flame zone. Open flame, as in grilling. Also, at a lower temp setpoint you are still going to get a higher heat at the grate surface because the heat comes up directly through the holes in the flame zone. Conversely, when using the solid pan the heat is more diffused and can only rise through the vents around the perimeter.So flame zone is useless when the PB is not at full temp?