Ewing
did put himself between Bell and the 3-point line. That was the brilliance of the play D'Antoni drew up.
IMO Dunleavy put in Ewing because he was expecting Bell's man to have to fight through a bunch of picks. So, Ewing came into that play looking for picks. He positioned himself between Raja and the potential screeners, and looked to keep himself between Raja and his 'destination', presumably behind the 3pt line
at the top of the key.
I'm positive Ewing was never expecting Raja to get open without any help. Look at the elements required from Raja that play--the little push to get open, then catch the ball, turn and shoot in one motion, all while drifting towards the endline and keeping his feet between the sideline and the 3pt line. That's a Ray Allen-type play, not something you'd expect from a spot-up shooter.
D'Antoni put a lot of trust in Raja there, but he got a great shot as a result. What Dunleavy got was something he wasn't expecting.