25. Subject to regulations 26 and 27, where the variation agreed to is one falling within regulations 18 to 20 (additional cases), effect shall be given to the variation in the maintenance calculation by increasing the net weekly income of the non-resident parent which would otherwise be taken into account by the weekly amount of the additional income except that, where the amount of net weekly income calculated in this way would exceed the capped amount, the amount of net weekly income taken into account shall be the capped amount.