Agreed, but I tried that last night against a stronger team in the CL and won the first leg 3-1. He was playing a flat 4-3-3 so I thought DMCs would cover the most in zonal marking, and then needed 3 defenders, but only had 2 DCs remaining, so I played a DL instead of a left sided DC.

I would just write something like you need 3 defenders in any of the 5 defender slots.