I'm using the Pro Q Excel 20's. Very similar to the WSM 22's. My top grate runs about 20 degrees cooler than my bottom grate.
So from dome temp on down:
260 (ish) on dome thermo
280 (ish) on top grate
300 (ish) on bottom grate
Honestly, it's simple physics really. What level will be hotter, the one closer to the fuel source or the one farther away? Sometimes we overthink these things, did it for years.
Oh yeah, if your using liquid in the water pans, consider aborting that idea. It's another physics thing.