Boiling occurs when the partial pressure of vapor at the surface of the liquid in question equals the pressure of the atmosphere at the liquid surface. Do we agree on that? The flashpoint is reached when the partial pressure of the liquid in question forms an inflammable mixture with the air at the surface. A very simple way to keep this from happening is to cover the container with microwave-safe Glad wrap or equal. Leave enough slack so that the wrap lies at least partly on the surface of the liquid. There can be no contact then between inflammable liquid and air and the first evidence of boiling will be when the plastic lifts up. There will be no creeping of vapor over the side onto the nonexistent heating element. I have learned by experiment that the airflow through the heating chamber passes over the hot light bulb BEFORE entering the chamber.