Quad MxFE test cases JESD parameters


I was reading thorough the Quad MxFE user guide and was a little confused by the example JESD204C link parameters.


For example, in the final test case in the link above, we have 4 Tx / 4 Rx per MxFE. Looking at the Rx side, we have ADC JESD204C: Mode 29, L=4, M=8, N=N'=12. Giving the maximum line rate of 24.75 Gbps.

My question is: why in this case is M=8? We have 4 converters on the Rx per chip so surely M=4, giving a line rate of 12.375 Gbps.

What am I missing here? The same question also applies to the 2 Txs / 2 Rx test case, as well as the Tx side.