DON'T WORRY! Be happy.
Although, there shouldn't be such a big diff between the two.
Have you tested the dome thermo? When you are finished the cook and its cooled off, unscrew the thermo and test it by:
1) insert the probe in boiling water--note the temp. Then
2) insert the probe in ice water--note the temp.
If it reads 212 and 32, you're good to go. If its off by 10o, you
now know It's really 225, not 235 for example.
Or just don't use it and rely 100% on the mav. Test the mav the same way.
It's not unusual for the dome temp to be higher OR lower than the grate temp.