Endgame Raider Camps

[BattleFate]

Perhaps the raiders could evaluate threat levels of your base before attacking. If they see that most of the entrance areas of your base are highly guarded and defensible they will avoid those. But they see a wall off to the side which they can access easily, they bring in a few grenade toting guys with them, blow the wall up and enter your base that way. They avoid your most highly defensive areas while keeping most of their people alive for the assault. Avoiding having exposed areas like this is part of good base design, but not always possible.

Maybe they only use this type of strategy if there is a leader with them, so normal raider raids just attack what they want, but the leader will coordinate and plan a proper assault (or perhaps withdraw if it's determined an assault is impossible against the available defenses).