How you rub a 220 grit water stone on a 320 grit diamond plate hone will not matter. The larger 220 grit will reach the base of the 320 grit diamonds and abrade away the Chrome plating that holds the diamonds in place before the 220 grit is knocked loose. I'ts a simple "Mines bigger than Yours!" issue. The only way to flatten a 220 grit hone with a diamond hone without damage to the diamond hone is to use a coarser diamond hone such as a 120 grit or even coarser. Better yet as mentioned above, use a glass plate and wet/dry paper to do the job. Best way is to simply use the 320 grit diamond plate for honing and chuck that 220 water stone in the drawer where it belongs.

The primary reason for loose bind of the grit in such coarse water stones is that you want the grit to release as soon as it begins to dull... after all, you're trying to hog off metal fast and dull abrasives simply slow the process. The idea is that as soon as you have established the approximate shape you would move along to a finer grit and start to refine the shape so the rapid deformation of the coarsest hones is considered a necessary evil that can be lived with.

Christian