WDSMCAST only transfers the metadata and not the WIM file

Hi all.

I am making a custom WinPE deployment boot.wim.
I am using WDSMCAST.exe to connect to a multicast session.

I have a 2008 R2 server running WDS, and I have a multicast session setup.
When I run the command from PE, it connects to the multicast session, and transfers for about 10 seconds.
It completes successfully - during the process I can see the WDS server showing that a multicast is in progress.

However, the resulting file that I receive on my client machine is only around 1.5Mb, hence why it takes about 10 seconds.
This is obviously not the full image.

How can I get WDSMCAST.exe to transfer the full image so I can expand it locally?
My image is 11918Mb.

Thanks.