There are some hidden paths that can fit your cage wall:
(select Custom Pathing Map)
PathTextures\12x10Pen45Path.tga
PathTextures\8x8PenPath.tga
(Found them by using W3ModelEditor--->MPQ Browser)
And if this doesn't fit your Magic Wall either:
Creating a pathing texture for a Pathing Map is not that hard...you need just a few Painting Skills and a good program that helps you do that (PhotoShop...etc)
Check the size of your Magic Wall.Create a blank picture(or you can import some path textures from War3.mpq/War3x.mpq), resize it till it fits with the Magic Wall(16x16...12x12....8x8...) than start painting....fill the borders with Magenta Color(255Red+255Blue) so units can't pass through your Magic walls and Blue/Black color in the center so they can stay in the magic wall.
When you're done save the picture in .tga format and import it with Import Manager in your map.
(Hint
on't use Windows Paint to make the image....after you save the image it alters the colours and that's not good...)