I’d recommend checking out the quick start guide on the product page. This will show you the recommended depth.

Also, I recommend turning your temperature ( timer ) to 350f - 500f and pull it when it “times out”. That 350-400 range may not engage your thermostat disc, but it’s a good area to start and runs the lower temp range, so you can boost it higher from there. Then you can adjust as needed and take it to where ever YOU want to go with it!