I am surprised that there is no reply to this post. Remembering a posting ages ago on sheets and where to embroider them and all the many replies I would have thought this would have got you lots of answers. And after all that I have no idea on how to help you, sorry and have a flower

here is a guide for how to place your design,scroll to bottom you will see linens I think this is what you are looking for if not please let us know

I am interesting in this also. So to the top!

I unpick the stitching on the opening edge of a pillowcase and then embroider the edge, once finished the stitching I resew the pillowcase. The back of the embroidery is then unseen. Helen

These are 2 I have done, pillowcase with ducks for hannah with matching sheet embroidered same way and pillowcases for my linen set.
Helen