walk thru/under base walls

[Full Frontal Yeti]

Depending on the lay of the land you can be allowed to place walls, but the walls will not be "solid" in some way. Leaving an AI pathable gap you can't see between wall segments, or from the correct angle only, a visible gap between the wall and the ground.

In both cases a base wall and gate means nothing, units, both yours and enemies, just path right through/under the wall.
It is only possible to see the under wall gaps when the camera is positioned unusually low.

Most times you can't find out this is going to be happening until after you complete a wall and gate enclosure, and see units ignore the gate to just go straight line where they want to be through the walls.
Though clearly the segment gaps and ground wall gaps are specific, units do path around the walls to to get to the gaps.