8 – How to specify the file path for the private file system?

Environment: Shared hosting, Apache.

Home directory: /home/someuser

Website at: /home/someuser/public_html/stuff

I’ve spent 2 days trying to get this to work, and realise that as soon as I’m answered it will be blindingly obvious, but I’m failing miserably right now.

I have created a directory in my public_html directory called private_files with a sub-directory called stuff. Both have access rights 755.

I have edited settings.php to include the line:

# $settings['file_private_path'] 
= '/home/someuser/public_html/private_files/stuff';

I have cleared all caches.

The file system configuration page shows:

Private file system path

Not set

What stunningly stupid mistake am I making? Why is what I’m doing wrong?