In SS5C, the "SS5C Stone Wall Larger Corner" (both of them) are not symmetric. The north-south portion is not the same width as the east-west portion (in the same symbol itself).

There is only one "SS5C Stone Wall Large", and it only matches one of the above-mentioned widths. Therefore, no matter how you try to rotate, mirror or flip sections you can't match the width of the other section. You can scale it to about .27620 (eyeballing) to make it match, but it would be easier if the corner symbols had palisades of equal width.