Within Areas B2 and B3 on the maps in the Appendix to this Chapter, where a special permit by the City Planning Commission on a receiving site is sought pursuant to Section 89-21 (Transfer of Floor Area From Hudson River Park), and the bulk regulations of the underlying C6-4X District apply pursuant to the provisions of Section 89-11 (Use and Bulk Regulations on Receiving Sites), the floor area ratio for qualifying affordable housing shall be 10.0 within a Mandatory Inclusionary Housing area, and such maximum floor area ratio may be increased to a maximum of 12.0 only as set forth in Section 89-21.