20. Where child support maintenance is being assessed to support more than one qualifying child, the relevant income of each of those children shall be treated as that of the parent with care to the extent that it does not exceed the aggregate of—
(a)the amount determined under—
(i)regulation 3(1)(a) (calculation of AG) in relation to the child in question; and
(ii)the total of any other amounts determined under regulation 3(1)(b) to (d) which are applicable in the case in question divided by the number of children for whom child support maintenance is being calculated,
less the basic rate of child benefit (within the meaning of regulation 4) for the child in question; and
(b)three times the total of the amounts calculated under regulation 3(1)(a) (income support personal allowance for child or young person) in respect of that child and regulation 3(1)(c) (income support family premium).