As an extension, England are probably better targeting a classic dismissal of Smith and trusting the ball might do something off the pitch. To begin with last test, while Root made some pretty idiotic changes to the field, Smith never really looked 100% comfortable until England's bowlers blinked first. England need to accept he's a very good batter and isnt going to go straight for the bait straight away, but they need to win the battle of patience. He's most uncomfortable with that 4th stump line and the ball swinging away, so dont change from that line. Keep on asking him to play it 100 times a session, with a few inswingers to keep him honest, or maybe the odd fractional change off going slightly fuller or wider.
I think England seem to forget every test that his showing all three stumps and walking into shots style indicates a weakness on his pads. They then seem to forget that when Smith's score goes from 20 to 100 runs, 50% percent of his runs are tucks off his pads when they inevitably bowl to straight to him. Its like the bowlers wipe their memories after an innings and constantly fall for the same traps. That and those frankly embarrassing passages of play where Root moves half his field for the bouncer, and then you get nothing but shorter balls for a session.
Its a phantom issue. His head regardless of his all action movement is always straight. He plays that middle stump ball coming into him better than anything, but time and time again you see teams spending half his innings trying to get him to miss one. He isnt Shane Watson, his hands and eyes are much better than that.