My settings for the hair itself is for optimal realism, not for speed. Therefore, yes, the hair is set to Light emitter, Casts shadows and all that good stuff.

To recap the skullcap situation:

Visible unchecked: Hair roots exposed and not properly shadowed. If there is a visible part of any sort, the hair density has to be cranked to ridiculous levels to avoid showing too much skull, and even then the shadows near the roots don't look right. On the bright side, no IDL artifacts. This, by the way, is the same as parenting the hair props directly to the character (in this case, V4) rather than to a skullcap.

Visible checked, Light emitter on, Visible in Raytracing on in Properties; Transparency 1.0 feeding to a fully black transparency map: Great hair shadowing, especially at the roots, but varying levels of splotchy artifacts. Just how splotchy varies by playing with other settings.

So far as the difference that using the face's materials goes, the jury is still out, but it looks like it does have an effect, although I don't know why. I thought it would be the SSS, but the SSS pass still shows the skullcap area as dark. So I don't know.

At any rate, the bottom line for now is that using a skullcap set to Visible/Light Emitter/Visible in RT + full transparency results in much better looking root shadowing, but also results in artifacts. I guess this is probably why Vilters thinks the artifact issue with hair room hair is gone: he hasn't attempted to do what I've done here. For myself, the improvement of root shadowing is worth the splotches if I can blur them enough to make them look like natural shadows, but it obviously would be better if I could get those results without the artifacts. Hence all my experiments above.

Unfortunately, I'm almost thinking that the role that the skullcap plays in this case is unintentional, which would mean it may not work forever.

I say this because what is happening with the skullcap should also be happening when the hair is parented to the head without a skullcap (I think), and it isn't. Theoretically, if the skullcap is set to Light emitter etc and gives this sort of root shadowing, that same sort of root shadowing should occur if the hair is parented directly to the head (which obviously is set to Light emitter). But in fact it doesn't.

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Hardware: AMD Ryzen 9 3900X/MSI MAG570 Tomahawk X570/Zotac Geforce GTX 1650 Super 4GB/32GB OLOy RAM

Software: Windows 10 Professional/Poser Pro 11/Photoshop/Postworkshop 3