Why later Oliver Hazard Perry frigates used the long hull

Why were some Oliver Hazard Perry-class frigates built with short hulls and later ships with long hulls?

The later batch needed a little more length and volume, particularly to support SH-60 helicopter operations.

The class moved from an initial short-hull batch to the later long-hull configuration rather than building every ship to one standard. The dimensional change was only about eight feet, but it supported the revised aviation fit and operation of SH-60 helicopters. The panel compares that modest extension with the much larger growth of later Type 42 destroyers, which Britain did not label as long-hull ships. The watch point shows how a small dimensional change can mark a meaningful change in aviation capability.