Review miningRelevance
How well Apple matches your app to a search term. The half of ranking that is not metadata.
Metadata creates the association; relevance turns it into a position. What feeds relevance is behaviour: people arriving from that search installing the app, opening it, and staying.
If a word is in your title and you are still ranked 11-30, the problem is not placement but relevance - screenshots, the first-run experience and conversion rate are what matter next.