If you aim an infrared thermometer at a porous surface like a grill or grate, it will factor in the surface temp of whatever surfaces are visible through the holes of the grill or grate when calculating a final temperature for your reading.

To accurately measure the temperature of a porous grate or grill, place a solid surface like an iron plate or skillet on the grill, let it come to temperature, and measure the plate or skillet. Spray a little cooking oil on the plate or skillet to ensure proper emissivity.