Well, it sort of depends on how you set up the hair prop.

In 99% of cases, just follow the steps I described in my post https://www.renderosity.com/mod/forumpro/?thread_id=2946761# pp

And as @Kalypso added (THANK YOU FOR THIS!), if it's a hair >figure<, just follow her advise!

Re. your question about a posed figure:

If you've followed the steps as described above, then it doesn't matter which pose or which xyz translation your figure is at. You only need to zero your hair and the figure >once>, which is during the initial setup. After that it doesn't matter any longer.

Just select the figure and click the hair. It will parent "avtomatisheskiy" to the head, "whereever you lay your head" ;)

K