Michael, I took your first photo and circled your thermostat in red (see below). This is a thermometer of sorts that, based upon the temperature you set your oven at, turns your element off when the oven reaches the target temp. So if the peak oven temp is 270, the thermostat will allow the element to turn on until the oven hits 270 and then it will shut it off. Most thermostats control both the broiler element (top) and the bake element (below).
In other words, if you put the stone on the top shelf, preheat it to 270 and then try to turn on the broiler, because of the position of the thermostat, the broiler won't turn on for long- a few seconds, at most.
That's the bad news.
The good news is that the thermostat is a rod connected to a wire and can usually be removed from the clip or the entire clip can be removed. If you put the stone on the top shelf/near the broiler, unclip the thermostat and place it on a shelf beneath the stone, the stone will shield the thermostat and the broiler will stay on long enough to get a really nice bump in temperature. Once you partially remove the thermostat from the picture, there's no way of really knowing the temperature of the stone- so you'll need an infrared thermometer.
What's your bake time presently?
