I'll update the tutorial, I think though that 127 and 128 are close enough to not matter *too* much. Also Sinister, I mentioned setting it into an action and even have said action available in the tutorial.
that's because you can't overlay it without changing them. That's the whole idea, to change it. When you put a layer into overlay mode, it is essentially modulating each channel, by the channel above it. darker than middle grey, and it darkens it, lighter and it lightens it. If your photoshop overlay is only details, it…