update trace queries

Author: rtrieu

content/en/tracing/trace_explorer/trace_queries.md

@@ -106,7 +106,7 @@ Trace Queries run on traces indexed by the [intelligent retention filter][3] and
 {{< img src="tracing/trace_queries/trace_queries_base_data.png" style="width:100%; background:none; border:none; box-shadow:none;" alt="Flow showing where trace retention filters apply in the processing pipeline" >}}
 
 The intelligent retention filter is enabled by default and includes:
-- [Flat sampling][4]: Uniformly samples 1% of ingested spans.
+- [Flat sampling][4]: Retains all traces associated with 1% of ingested RUM sessions, plus a uniform 1% sample of ingested spans, ensuring correlation between frontend sessions and backend traces.
 - [Diversity sampling][5]: Retains a diverse set of traces to maintain visibility across environments, services, operations, and resources.
 
 Both Flat sampling and Diversity sampling capture **complete traces**, meaning all spans within a trace are indexed to ensure accurate results in Trace Queries.