gzip -l big_archive.tgz
         compressed        uncompressed  ratio uncompressed_name
       617736021001          3613347840 -16995.9% big_archive.tar

As you can see, the ratio field is producing an incorrect result.  I'm not sure if this is because the archive is too big or what.  It was generated via the following command in quotes:

"tar -cv /path/to/folder/big_folder | gzip --rsyncable > /path/to/big_archive.tgz"

gzip version: 1.9

Hardware: Dell R720 Poweredge Rack Server

OS: Debian 10 buster

Kernel: Linux 4.19.0-18-amd64
Architecture: x86-64

Best regards,

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