I've found that the factory therm in my WSM is a good guide, but can vary up to 30 degrees from the grate temps, also the top & bottom grates can vary up to 20 degrees. If you are looking for very accurate temp control then you need at least 1 probe on the grate 2'-3' from the meat. After a couple of smokes in my WSM (got to get the inside coated with mojo) I put probes on both grates & recorded the temps every hour for 7 hours, along with the lid therm temp reading. I can now know the temp variations between the grates. In other words if the top grate is reading 225, then I know the bottom grate is in the 210-215 range. Also, the WSM tends to be hotter around the edge. I would experiment with your new one to see what the temp differences are. I think they may be different on your smoker, due to air leakage around the door & bottom, middle, & top sections. Every smoker is a little different, even the same model.