35.The provisions of this paragraph apply where the non-resident parent has a flat rate liability because he is in receipt of a prescribed social security benefit, pension or allowance or he or his partner are in receipt of prescribed benefits or he or his partner receive prescribed benefits and both are non-resident parents.
Sub-paragraph (2) provides that where a non-resident parent shares the care of a qualifying child for at least 52 nights in total during a prescribed 12 month period, his liability to the parent with care of that child will be nil.  However, his liability to any other parent with care to whom he is liable to pay maintenance will remain.
Part 1: Child Support. Commentary on Sections Schedule 1: Calculation of weekly amount of child support maintenance Paragraph 8: Shared care – flat rate