reds on DL/DR --> DML/DMR likewise.
reds on MR/ML (like 4-4-2 flat usually uses) -> AML/AMR
DML/AML and DMR/AMR plays in the same field zone, so if your defenders are better you tend to stop almost everything in there. An additional blue arrow on your dmc can make him help the remaining 2 DCs if you are facing 2 STs. or the 2 DCs can dispose of the lone st.
Additionally, DR/DL get aid from the dmc on the sides.