Here is a generic cut-a-way of a
WSM set up to smoke with a water pan and two racks for food. I think the photo is of the 18.5" but it's the same (only a little bigger in diameter). This appears to be a
WSM with the original, smaller, water pan and the newer ones have a little less room between the bottom of the pan and a full fire ring of charcoal.
Your water pan should be smaller than the 22.5" grates as there must be a gap around the outside of the water pan so the heat and smoke can flow upwards. I don't know the dimensions of the 22.5"
WSM's water pan, but if it is fitting on those tabs/brackets, it sounds like it is the right size. The top of the water pan should be just below the lower rack when it is installed. The lower rack should not be sitting on the water pan and the lower rack should have it's own set of steps on the bracket to sit on. Also I know in the 18.5" version the top rack is the one with the installed handles and my lower rack did not come with handles. I added some stainless wire to make two handles on mine, but mine is a 2005 model so that may have changed in the re-design for the 22.5" version.
Edit......
Found another photo of a cut-a-way 22.5"
WSM. So this should be pretty accurate for your model