FWMH - Improve FlushInterval Javadocs

spring-integration-file/src/main/java/org/springframework/integration/file/FileWritingMessageHandler.java

@@ -299,7 +299,9 @@ public class FileWritingMessageHandler extends AbstractReplyProducingMessageHand
 
 	/**
 	 * Set the frequency to flush buffers when {@link FileExistsMode#APPEND_NO_FLUSH} is
-	 * being used.
+	 * being used. The interval is approximate; the actual interval will be between
+	 * {@code flushInterval} and {@code flushInterval * 1.33} with an average of
+	 * {@code flushInterval * 1.167}.
 	 * @param flushInterval the interval.
 	 * @since 4.3
 	 */

src/reference/asciidoc/file.adoc

@@ -640,7 +640,7 @@ However, this can cause data loss in the event of a failure.
 Several flushing strategies, to mitigate this data loss, are provided:
 
 - `flushInterval` - if a file is not written to for this period of time, it is automatically flushed.
-This is approximate and may be up to `1.33x` this time.
+This is approximate and may be up to `1.33x` this time (with an average of `1.167x`).
 - Send a message to the message handler's `trigger` method containing a regular expression.
 Files with absolute path names matching the pattern will be flushed.
 - Provide the handler with a custom `MessageFlushPredicate` implementation to modify the action taken when a message