1. These 2 options don't "enable" passive mode. I'm sure you read https://code.google.com/p/pyftpdlib/wiki/Tutorial which says it is just overriding default behaviour.
2. I don't think "passive" should be in uppercase. I know the command "PASV" is usually written in uppercase, but not the word.
2. Please put a period at the end of the sentence to fit in with the rest of the file.

Suggestion:

    # Restrict the ports to use for passive (PASV) data transfers.
    # Ports will be chosen by the operating system if this is not defined.