If I understand correctly what you're saying, the lid vent is reading about 20 degrees hotter than actual grate temp. This makes sense to me, as lid thermometers always read hotter (heat rises) but because that lid thermo is halfway between heat and food, it isn't reading any higher than 19 degrees "too hot."
I think if you spun the lid so that the thermo was over the food it would have been more accurate, but it's academic: you'd want the vent over the food of course.
Use caution when putting any instant-read or probe on or near a cook grate. The metal could be a hotter temp than the air immediately above it, and probes aren't designed for anything beyond about 550.