Boosting per field and index when searching multiple indexes

I am searching multiple indexes. I want to be able to boost specific fields of specific indexes. I could not find a way to specify boost for a field of a index. I found examples in documentation where boosts are specified for field and doesn't mention anything about an index. This could cause issue if searching multiple indexes and just want to boost a field named "MyCode" in "IndexA" and not the field by same name in "IndexB".

Please help!

Maybe the indices_boost part in a query helps, see Search API | Elasticsearch Guide [7.13] | Elastic (does not support boosting a pair of index/field, just an index though).