Subject: @Which not supported from back-end agents
@Which folder only displays with the client UI open. It is not supported via back-end agents. You should edit the agent and change the view it operates on or you can create an agent using the LotusScript back-end classes and programmatically create the collection you want sent.
NOTE: The agent is not defaulting, for me, to any particular view. It seems to choose the first view it find in the NSF. You can change this selection when you create the agent.