Here's an image showing the path: http://imgur.com/Yj1NY9A
So as you can see, the path passes at the edge of the blocks. Why does that happen and how do i fix it?
Take a look at this wiki article.
To explain: The path is in the center of each 4x4x4 voxel, however, the wall takes up almost half of the voxel, and not the whole voxel. I would recommend expanding the size of the wall about 2 studs, to fix this issue.