You may have a right of appeal but I'm not sure why you think that salary and dividends would be treated separately for child maintnance purposes because they aren't. Can you explain your situation a little more.
The rule is that gross income less pension contributions is taken into account. The way the law has been framed presently is that dividend income doesn't have to be put into the calculation but the recipient parent can apply to the CMS for a variation of the calculation so that dividend income is included and from your narrative that is what has happened here. Frankly the rules don't make a lot of sense as most company directors take their income at least partly by way of dividend so why the CMS standard formula doesn't account for this is less than logical. The other sting in the tail is that if you don't reach an agreement and the payments are made via CMS, you will be charges an extra 20% in charges and your wife will pay 4% in charges.