I'm afraid i can't really follow. Assuming we are talking about accurate quality work.
So this is the head of an adult G8 female i'm working on, standing approximately 175cm tall (40% height morph).
The hair is "2021-15" for G8F by OOT with all adjustment morphs on zero.
View attachment 4082260
As we can see, the scalp mesh is clipping like crazy with the head topography. In particular on the cheek bones, and the lower head backside / neck region is even worse with large holes in the scalp.
And this is the forehead in wire texture shaded mode.
View attachment 4082263
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View attachment 4082264
The right pic uses a facial animation. Now the scalp mesh massively clips with the forehead, which causes the black artifacts in renders.
And that is a harmless issue which can be fixed with a bit of headsize and forehead depth from the built-in OOT morphs.
How would this ever work when trying to manually move the hairstyle mesh around?
Loading the basic G3F model, loading the same 2021-15 hair for G8F (not fitted to the character).
Setting the G3F to 40% height, then trying to make the hairstyle fit:
View attachment 4082298
This isn't even matching the character shape by 1%. It touches in a few spots, while most surfaces have either no contact, or are inside the head.
The figures are simply incompatible just based on their shape differences.
Can't even imagine how this would ever work with with fully customized characters.
Some hairstyles don't even come with any adjustment morphs at all, like those from SdeB.