For zoning lots in R4 or R5 Districts, without a letter or number suffix, utilizing the predominantly built-up area provisions of Section 23-71, inclusive, the following height and setback modifications shall apply:

1. in R4 Districts, the height and setback regulations applicable to an R4A District set forth in Section 23-421 (Basic pitched-roof envelopes for certain districts) shall apply; and
2. in R5 Districts, the height and setback regulations applicable to an R5B District set forth in Section 23-422 (Basic flat-roof envelopes for certain districts) shall apply.