Examining the syntax of the config.pl file seemed to provide the missing link. 
Just in case someone else comes across this question, attached [this time] is 
the configuration that is working in the GUI and here are the corresponding 
entries for /etc/backuppc/config.pl to exclude some folders within a share:

$Conf{BackupFilesExclude} = {
  '/home' => [
    '/*/Dropbox',
    '/*/Downloads'
  ]
};

...
$Conf{RsyncShareName} = [
  '/home'
];

backuppc.png
Description: backuppc.png

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