When the Lamanite leader regroups, he heads for a location that he assumes will be an easier target. His information on these weaker points would have come from the Zoramites in his command (if he was not himself a Zoramite) since the Zoramites had been placed in important positions in this army precisely because they should have known the weaknesses of the Nephite cities (Alma 48:5). Moroni has thwarted this insider information by changing the physical defenses of cities, and by reworking the lines of defense.
Hugh Nibley’s experience in the military intelligence community gave him a unique perspective on Moroni. In particular, he notes the similarity of Moroni’s defensive scheme to modern concepts:
“Moroni’s defenses were based on a series of strong points, being a defense in depth, as modern defense-lines are; beside specially placed “small forts, or places of resort,” towns and cities on the line were also converted into strong points (Alma 48:8). Such an arrangement can take the momentum out of any military steamroller and slow down or stop any attacking force, no matter how formidable, by forcing it to reduce one strong place after another or else bypass the fortifications and thereby leave dangerous enemy forces in its rear to disrupt communications and launch harassing counter-attacks on invading units.” (Hugh Nibley, Since Cumorah, 2nd ed. [Salt Lake City and Provo: Deseret Book Co., Foundation for Ancient Research and Mormon Studies, 1988], 306.)