To put it simply: Australia, NZ and SL are almost through. Therefore, it is in Bangladesh's interest if they keep on winning every match they play [ against each other it does not matter - unless we don't want Australia as No. 1 ]
As SA still have to play NZ, ENG and WI then, if they win against ENG and WI they are more or less through [ compared to Bangladesh on a better likely run rate ].
So, we want that between SA, ENG and WI , they each win once amongst themselves. Since all have already played Ireland whom we have not played yet.
The reason I was saying that we don't want Australia to finish top, is because No.1 plays No.4 in the semi final. [ Wishful thinking ? ]
1.We want AUS, NZ and SL to win all remaining matches. Amongst themselves, it would be best if AUS loses.
2. We want SA, ENG and WI to win once amongst each other. Then if Bangladesh win all 3 , we are definitely through. With 6 points , we would still have a chance as only SA will have 6 points and one of ENG and WI [ assuming we beat Ireland ]. Hopefully, no one can pile up huge positive NRR's as they all will have played Ireland.