Been playing this too much. Got a score of about 170,xxx,xxx. Can't get to that 2 million mark.
Something that will get you to at least 120 mil is using blue blue red red green with one blue turret within range before the rest are. upgrade damage on all and that way the blue will send out a mine with friggin lasers for each set if the other turrets dont see it first. Place the red first just out of range then the blue closer and expand its range....