Fulltext search rank setting

[pioz]

I've a scope like this:

pg_search_scope :fulltext, against: [:firstname, :lastname, :middlename, :wholename, :title, function],
                using: {
                  tsearch: { prefix: true },
                    trigram: {
                      :threshold => 0.2
                    }
                  }

When i search with the string GRO I would like that the records that match the exactly word GRO have rank higher than records that match words like GROUP (group contain gro).

Any idea, if there are some settings to do this?