No matter what you do, salt added to fresh cabbage will draw out moisture so some dilution of the dressing is to be expected. If you really want to minimize it, you can take the extra step of salting and draining the cabbage before proceeding with the recipe. To do that, add the chopped cabbage to a fine mesh strainer placed over a bowl. Very lightly sprinkle the cabbage with salt and toss so that it's mixed well. Allow it to sit for at least 30 minutes and up to one hour. Discard the liquid that collects in the bowl. You can take an additional step then and spread the cabbage on a layer of paper towels to remove as much additional moisture as possible. Continue with mixing the dressing and finishing the recipe.