DefaultRoot in proftpd virtual host not going to subdirectory

Question

I'm attempting to mimic a client's ISP environment using Ubuntu 12.04 in VMWare Player. FTP is with proftpd. All proceeds nicely until I get to having ftp open in a subdirectory of the user's home directory. So for a user foo with home directory /home/foo & subdirectory /home/foo/bar, I want ftp to open in /home/foo/bar. The contents of /home/foo should not be visible. Unfortunately, ftp opens at /home/foo.

Here's what I've got in virtuals.conf:

<VirtualHost foo>
  ServerName            "foo's FTP Server"
  DefaultRoot           ~/bar/
  Port              21

  MaxClients            10
  MaxLoginAttempts      1

  # DeferWelcome prevents proftpd from displaying the servername
  # until a client has authenticated.
  DeferWelcome          on

</VirtualHost>

I've tried various combinations of syntax on the DefaultRoot directive with no luck. The proftpd log shows the chroot to /home/foo, not /home/foo/bar.

If you haven't guessed by now, I am very new to Linux, let alone Ubuntu. But all of my reading suggests that the above should work. I am certainly missing something. What?

Thanks in advance for sharing your wisdom.

George