Just to support what's already been said. Until the KK is heat soaked, there's generally a noticeable difference in temps between the dome and the grill surface, particularly on indirect heating. As the lid heats up, it will radiate heat back toward the main grill (assuming you're using a heat deflector) and they will equilibrate to within a few degrees. If you are cooking direct (no deflector) the temperature difference will remain, but be smaller (on the order of 10 degrees or so). Bottomline - don't sweat it, if you've checked your probes and they are calibrated (which you did).