Hi!
did you try the settings mentioned here?
Wherever (dark) hair still is hard to scan I use dry shampoo FTW.
Remember: after first scanning the face (i mostly use auto exposure) , before scanning the hair you also can pause the scan, turn auto exposure off and manually increase exposure to your likings so hair is picked up better and than continue scanning.
You can also make two scans, one for the face with one settings (like near mode, high accurracy) and second one for the hair (maybe lower acurracy and dark mode?) and merge these two scans in the post processing. Just make sure you have enough overlapping area in both scans
Give it a go and let us know if it works for you, too.
cheers