I just ran some non-scientific tests with compression quality set to 11 (max), and these were the results:

frogfind.com - default: 3 messages :: new: 3 messages

lite.cnn.com - default: 43 messages :: new: 44 messages

text.npr.org - default: 8 messages :: new: 8 messages

"NFL Suspends 5 Players for Gambling" article: default: 15 messages :: new: 15 messages

Seems like either I haven't properly implemented the dictionary, or the default compression level is already set to max.