Current calculations are not based on any realistic situations and are wholly unfair to the non-resident parent, especially if the non-resident parent has financial responsibilities for another child/children living with them.
I propose a more realistic calculation as follows. Total net income of non-resident parent, minus mortgage/rent, council tax and all utility bills then this total is divided by the number of people living in the house hold + number of children supported by the non-resident parent. This calculation is based on the fact that if the child/children WAS living with the non-resident parent, this is how much would be available to spend on them.
I appreciate this will take longer in calculating the account of the non-resident parent but surely that is a sacrifice that should be made to ensure everyone and every child is treated evenly and fairly.