For the purposes of paragraph (a) of the definition of Commonwealth superannuation scheme in section 5, the normal earnings of a person who has chosen a Special Rate Disability Pension would be worked out under Subdivision D of Division 4 or 8 of Part 4 of Chapter 4 if the amount worked out under that Subdivision is greater than the amount worked out under Subdivision C of Division 4 or 8 of Part 4 of Chapter 4.