I personally think Raina's dismissal was the turning point. Having scored 50 and with Tendulkar on the other end, and a RRR of 5.5, he should have been a little less flamboyant in his batting. It's much easier for a settled batsman to keep the RR going and take the team to the end, than to expect new batsmen to finish the job. There was really no need to go all out at that stage.
I dont think the RRR ever dropped to 5.5, but I agree with the rest of your post.