HI,
I believe you misunderstood the Blade network concept,
if you connect the 6120 switch in Interconnect Bay3 & 4, then there should be equaling Mezz card installed in server.
If you do not have the network card installed in mezz slot , then any switch installed in any interconnect bay (other than 1 & 2) will not be helpful.
Hope this helps you answer your query.
Regards.
HPE Server support