Do you not believe in a defensive 3? If so I'm interested to know why not.
I've played with defensive 3 most of this season except when bans or injuries or the opposition tactics may require a change. I've only conceded 9 league goals. I do play mostly with two DM though, when I have a back 3. If I have a back 4 I go to 1 DM, or sometimes none at all.