autovacuum_vacuum_insert_threshold

The fixed part of the insert trigger (default 1,000). On append-only tables the recipe mirrors the dead-row side: insert scale factor 0 and a threshold sized to about an hour of the insert rate. Pair it with a low vacuum_freeze_min_age so the insert-triggered vacuums actually freeze what they visit: pages an append-only workload writes once and never touches again.