The optional provisions for sky exposure plane buildings set forth in Section 23-73, inclusive, may be applied to zoning lots in Commercial Districts mapped within, or with a residential equivalent of, R6 through R10 Districts without a letter suffix, except that such alternative provisions shall not apply to zoning lots:

1. in Commercial Districts mapped within, or with a residential equivalent of, R6-1, R6-2, R7-3 and R9-1 Districts;
2. in Commercial Districts mapped within, or with a residential equivalent of, R8 Districts without a letter suffix in the portion of Community District 9 in the Borough of Manhattan located north of West 125th Street;
3. located in the Limited Height Districts; or
4. in C4-2 Districts in the Borough of Staten Island.