Can multiple stream Id requesting the same data be encoded as 1 message and sent to ADH to handle fanout ?
Do you mean requesting the same item with different stream IDs to ADS with ETA (UPA)?
If you request the same item with different stream IDs to ADS with ETA (UPA), you will get the following error message.
Received Item StatusMsg for stream 6 State: Closed/Suspect/Already open - text: "Item was reopened under new stream."
However, you can use RFA, ETA (ValueAdded with WatchList enabled) or EMA to request the same item because those APIs are able to handle fanout on behalf of the application.