The Planning Board is hereby authorized to require clustering of residential units as outlined in Chapter 234, Subdivision of Land, of the Code of the Town of Ithaca, where clustering will further the purposes of the Conservation Zone, subject to the requirement with respect to the Conservation Zone along Six Mile Creek, that where feasible, on the southwestern side of Six Mile Creek (i.e., on the Coddington Road side of the Conservation Zone), dwelling units shall be clustered between the former railroad grade and Coddington Road, in order to preserve the natural characteristics and scenic views of the lands adjacent to Six Mile Creek and the city watershed properties. In such cases, the same number of dwelling units that could have been built on that portion of the parcel between the former railroad grade and Six Mile Creek under the above density requirements when feasible shall be transferred to the portion of the parcel between the former railroad grade and Coddington Road. This provision shall not apply to parcels which are situated entirely between the former railroad grade and Six Mile Creek.