Hi Tommy,
Well, the function is simply not executed for the indexed searches, the hook is not applied to them. The problem is not with the code, but the fact that the asp_change_query_directly hook does not exist for indexed queries.
Even if we added that hook there is no way to make that code work with it, as the index does not store post parent and status information, so subqueries/table joins would be required – and in that case the queries are no longer in indexed mode, and will result in the same peformance as the regular queries (due to the table join/sub queries).