I think India should forget about run rates and topping the group and concentrate solely on winning the match by whatever
legitimate means possible. It does not matter if they play the most defensive and boring cricket (not that such an approach is likely to work with the mercurial Sri Lankans

), but they have to WIN. Now that Bangladesh are too low on their own run rates to make a difference, India should only worry about beating SL somehow or the other. Once they are succesfully through to the next stage, they can look at the teams they then have to play and plan their strategies afresh.