This.

It's 100 miles of land & sea borders. Plus the airport zone. The airport does not create a new 100 mile zone.

For example, ATL is not within 100 miles of a sea or land border, so the CBP zone is just the airport, not the 100 mile circle around the airport. But, ORD and LGA are both within 100 mile zones.

Of course, it's all kind of a moot point, as the current administration seems happy enough to deploy immigration forces nationwide and Congress is spineless and incapable of pushing back.