I would also recommend that you take a look at some articles regarding Lucene scoring, as it is quite complex:
- https://lucene.apache.org/core/3_5_0/api/core/org/apache/lucene/search/Similarity.html
- http://www.lucenetutorial.com/advanced-topics/scoring.html
You could consider boosting fields/terms to adjust the results as well: http://www.bizstream.com/blog/march-2017/boost-kentico-smart-search-results-relevance-score