Tune zstd parameters to decrease memory usage during streaming

Using the cached-microdesc-consensus that is:

valid-after 2017-11-21 11:00:00

I get the following results:

$ zstd cached-microdesc-consensus
$ gzip -9 cached-microdesc-consensus
$ du -h cached-microdesc-consensus*
1.9M	cached-microdesc-consensus
564K	cached-microdesc-consensus.gz
576K	cached-microdesc-consensus.zst

It's only 2% larger, but I thought zstd was meant to produce smaller consensuses than gzip? Or did I get the compression settings wrong?