The amount of the post-commencement supplement for any post-commencement period in respect of which a claim under section 321 is made is the relevant percentage for that period of the reference amount for that period.

If the post-commencement period is a period of less than 12 months, the amount of the supplement for the period (apart from this subsection) is to be reduced proportionally.

Sections 325 to 329 have effect for the purpose of determining the reference amount for a post-commencement period.