Thanks Mike, Your query works fine
However I'm not sure how to add this in a bigger function_score query.
I mean I have a function_score query which wraps the main query (a filtered one) and have several functions with a max score_mode.
Ideally I would like to add the nested value score as a new function. But it seems that to access to tracking.rating in the function, the function_score has to be in the context of a nested query to work.
So basically the question having a function_score query, is there a way to add a new function which access to tracking.rating of a particular user, without putting the whole query inside a nested query?