How can I request reverse delegation for my ASSIGNED PI IP range which is smaller than a /24?

If your IP range is: X.Y.Z.A - X.Y.Z.B, please create the following SOA record in your name servers:

A-B.Z.Y.X.in-addr.arpa

Afterwards, send the domain object A-B.Z.Y.X.in-addr.arpa to <ripe-dbm _at_ ripe _dot_ net>.

We will delegate the above zone to your name servers. Additionally, we will create CNAME records in our name servers for each of the corresponding IP addresses in this range, as follows:

A.Z.Y.X.in-addr.arpa. 432000 IN CNAME A.A-B.Z.Y.X.in-addr.arpa
[...]
B.Z.Y.X.in-addr.arpa 432000 IN CNAME B.A-B.Z.Y.X.in-addr.arpa

From this point on, you can create your PTR records as:

[address].A-B.Z.Y.X.in-addr.arpa