Exactly… The diffuser now sits at the bottom of the pot with the modified grate and you use the steam plate recess for your 3rd cooking grate allowing for extra cooking space. . So now you use the pots lid to raise it a few inches out of the lower part of the weber allowing more charcoal room. Best of both worlds.
But back to Adams build. There really is no wrong way. The way you want it built is the best way! b