Within Areas B2 and B3 on the maps in the Appendix to this Chapter, where 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 of the underlying district shall not apply. In lieu thereof, the maximum base floor area ratio 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 (Transfer of Floor Area From Hudson River Park).