There are lots of factors in play here. For example, long posts take more space than short ones. As a fellow lusófono I know how crazy verbose our language can be. I see your data comes from an import. Some artifacts, like posts with 5 level-deep quotes aren’t common in Discourse but are found in your site because of the import. Our language also matters as a ç takes double the space of a s.
I do believe we don’t change the PostgreSQL default, and the posts.raw column goes to TOAST and is compressed.