I looked into it and could reproduce your results.

FWIW I tried best compression for gzip

use IO::Compress::Gzip qw(gzip :constants);
sub compgzip
  {
      gzip \(shift) => \(my $output),
        -Level => Z_BEST_COMPRESSION;
      $output;
  }
use IO::Uncompress::Gunzip qw(gunzip);
sub uncompgzip
  {
      gunzip \(shift) => \(my $output);
      $output;
  }
[download]

and got

------------------------------ Compression by gzip/gunzip

length of            data 210168
length of compressed data 42210
compressed to 20.1%
MATCH
[download]

update

I noticed that -Strategy => Z_RLE already led to compressed to 20.9% so my theory is that your runs are so homogeneously distributed that the second phase Huffmann couldn't squeeze more than 0.8% out of it.