Different files can be compressed to different sizes.
For example, if you compress bitmap or text files, you'll get high results.
It also depends on compressor program and its method of compression (just use 7Zip instead of WinRAR and you'll see that it compresses much better).
Recently I've found KGB Archiver, which is probably the best high-compression tool today.
I couldn't believe that file which size is ~1GB can be compressed to some MBs, but it did!!
So 19% compressed archive seems nothing to it ;)
It uses PAQ6 algorithm, thus it needs a lot of CPU and RAM to compress.
Now it's an open-source project and is located in SourceForge. You can download it here.