So explain why there is no area at the top of the head that would indicate where the shroud would wrap over the skull as it would if it was real...
The simple answer is that there is. The claim there isn't comes from skeptics who have not examined the Shroud itself and make assumptions not based in fact. What they claim to be the joining of the two images is in fact a water stain. There is, in actuality, a space approximately 6-8 inches where there is no image between the frontal and dorsal images at the head where the cloth draped down.
You can see this is obvious in this paper with full interactive photograph in which you can magnify that area. Look for yourself.