Why does the % charge differ to the provider charging brochure on an Ex-post review?

With the Ex-post review screen, the percentage cost is calculated from the monetary (£) figure.  The monetary figures are calculated using the balance of the product and any growth on the balance. The percentage derived from this monetary figure may therefore differ slightly from a provider charging brochure, or any special deal rates for new illustrations as the growth is considered. E.g. The charges may vary with investment growth.