Archive not installable by NPM

[justinmc]

I'd like to use this package to create an archive of my own package that is installable by npm (the docs explain that npm can install from a gzipped tarball). However, npm is unable to read the archive output by grunt-contrib-compress with the following settings:

"options": {
  "archive": "path/to/mypackage.tgz",
  "mode": "tgz"
},

Running tar -cvzf on the same exact folder that I'm using with this plugin DOES give me something that can be installed with npm. Am I missing a setting or will this not work?