It needs to align along the same point of the C seat edge in the last row of CE, due to the reduced width of the B middle seat. There is a curtain between CE and ET, so if the trolley is being push slightly through the curtain, and the ET seat was not aligned, the trolley would bang into kneecaps of the person sat in the aisle seat. If the middle seats are fixed throughout the aircraft then this logic does not apply.