The Inner Glow effect is a filter that allows to soften the edge while keeping a clear line of the main silhouette at his center. It is heavily used by Blizzard and many other stylized studios to project decorations and text to an high poly sculpture with a stylized crack look like if a dagger was used to sculpt it. Michael Vicente has made a tutorial about this technique in a PDF: https://www.pearltrees.com/s/file/preview/139604217/OrbBevelTIP.pdf or in a video: https://youtu.be/eGHU8DI6fo4?t=5183
I try to achieve this:
It is important that we get only thin lines and not holes in more complex and wider areas. If we look at the displacement horizontally it should look like a V with a thin tipping point.
And here is what he gets by projecting it, as you can see there is just a think line at the center and the depth is flat:
The final result after using the Polish modifier of ZBrush:
The source image for your tests:
With the Inner Glow effect: