This seems to be a real art and I've seen many a wig that hasn't been undercut well, so the hair that's supposed to look like baby hair around the perimeter (particularly at the nape) looks very unnatural. However, I've also seen pictures of a couple of really good examples and so I'm on a quest for more information!
Some of the bad examples I've seen are that the hair has been cut too short (like 1-2 inches long)or, although the length of the undercut hair is OK (so it's easy to pull down when the wig is worn tied back/clipped up), it's cut at all the same length, so still looks wrong. Maybe part of the problem is the hair texture and bio hair is generally not only finer around the hairline, but the hair will be tapered.
Is anyone out there happy with the way their wig has been undercut? If so, are you happy to share photos and info on who styled it for you?
Jaye