#2 Cramp midfield, force the defenders to play it long
Now, it'd only be natural of you to think of me as a fool - if Roma, and their brilliant midfield trio, cramp midfield, they'll have to push up the pitch to stop Liverpool's midfielders receiving the ball at their feet. Having advocated that the defence sit deep, this would leave acres of space in between midfield and defence; usually a suicidal ploy. If they'd done it against Barca, for example, they'd not be here at all... but Liverpool lack what Barca had, what most teams have, a creative attacking midfielder.
Liverpool's forward line is most dangerous when running in behind defences, not running at them - and such a ploy would stop them playing their natural game. Once the defenders start playing it long, as long as the Roman line is in place - those three forwards are not winning any duels in the air against the Roman defenders.