It looks like you're new here. If you want to get involved, click one of these buttons!
Don't start closing the bottom vent and the daisy wheel either when you place the plate setter. I leave my vents fully open when I place my plate setter, due to it taking longer to reach my desired temp. I start closing my vents when my desired temp is reached.
The BGE fire is air flow controlled (assuming you have enough lump and got it going). So, temperature control (aka fire volume) is a function of the amount of air flow through the bottom and out the top. You can control by top or bottom vent or combinations of each (preferred for low temp cooks). The only way a fire goes out is too little air-flow (thus the above posts about clogged grate holes) but adding a platesetter or anything else will not impact the fire volume-you will see a dome thermo temperature change downward due to the cold mass but everything will return to stable conditions-if all was stable before.