There is another similar article where they tested a different search engine:
http://www.searchtechnologies.com/querying-indexing-cloudsearch
Some takeaways:
* Considers longer articles more important
* Considers shorter titles more important (aka Germany vs List of German Corps in World War II)
* Some hand tweaking ended up with the formula: text_relevance + 40.0*log10(content_size) - 15.0*log10(title_size)
* defined a per-document boost from 0 to 10 based on which namespace something belongs to.
* tweaked formula into: ext_relevance + (log10(content_size)*(doc_boost == 1 ? 25.0 : 40.0)) - (log10(title_size)*15)