Minecraft wiki entry for Historical_effects, associated text: Hitboxes beyond this point become very strange, and virtually non-existent in some cases. Assuming this distance is exceeded on only one axis and in the positive direction, a fence at a multiple of 4 coordinate will have an extremely thin hitbox at the negative side of the fence. A fence at a coordinate one more than a multiple of 4 will have no hitbox at all, one at an even, non-multiple-of-4 coordinate will again have a thin hitbox at the negative side, and one below a multiple of 4 will have its thin hitbox at the positive side. The image to the right showcases the solid faces approximately marked by signs.