I have a 2-socket R1208WFTYS system with the latest BIOS (00.01.0014) and it seems that there is a bug/inconsistency in regards to sub-NUMA activation in BIOS.
If I set "sub_NUMA Cluster" to "Enabled" and leave "IMC Interleaving" to "Auto", which suggests that BIOS will use the most appropriate settings (which has to be "1-way interleave"), then sub-NUMA is not activated - I see only two NUMA nodes (one per socket), whereas if I set "IMC Interleaving" to "1-way" explicitly, everything works as expected - I see 4 numa nodes (two for each socket).
So, since "IMC Interleaving" setting is tighly coupled to "sub_NUMA Cluster", "IMC Interleaving" should be removed altogether or at least "Auto" mode of it must be coordinated with "sub-NUMA" settings.