Dome/lid thermometer on WSM UNDER-reading???

[Zippy]

I have in the past (and still do) totally ignored lid thermometers, as I started out q'ing on a cheapo offset and the lid thermometer on that thing used to over-read the maverick on the cooking grate by 90-100F at times.

Since I have had my WSM (the larger size), I have noticed that the dome thermometer under-reads the temperature that my maverick probe gives at the cooking grate. I found this quite surprising as I would have expected it to over-read not the opposite. I have tested both thermometers in a pan of boiling water and there doesn't seem to be an issue with either's accuracy.

So I guess my questions are, for those that cook on a WSM or equivalent bullet smokers...

1) Do you use the dome thermometer at all as a reliable guide to cooking temperatures?? I haven't yet, but if I did i'd estimate the temps at my cooking grate would be 25-50 above where I try and get them (around 250F). I can never tell if my ribs are slightly over or under done, but they are never quite as tender and bite-off-the-bone as I want them, and I wonder if this is a solution.

2) Where/how do you position your maverick cooker probe?? I slide it into the bracket it came with so that it sits about 1 inch above the cooking grate in the centre of the cooking grate. Is this right/wrong for getting the magical 250F I want? Again, this is all in pursuit of that elusive perfect rack of ribs.

Thanks for reading, any help/advice appreciated as always.