Using hba_file parameter and relative path

In going through some parameter file cleanup and re-factoring, I've been
using the hba_file parameter to specify a non-standard file location. I
tried using a relative location, thinking it would be relative to $PGDATA
but in actuality it is relative to the pwd of my bash session that starts
the database.

For example, if I'm in /tmp when I run "pg_ctl start", it will look for the
hba_file value under /tmp. If I change to $PGDATA/pg_log, it will look
under there.

Obviously I can change to an absolute path and not worry about it, but I'm
curious if this is the intended behavior. Why would we want that hba_file
value to be relative to something as volatile as pwd?

FWIW this is Postgres 9.6.5 on CentOS 7.3.

Don.

--
Don Seiler
www.seiler.us