The scoring bonus is applied when you have more than a single stream of runoff. So, if you found a location that eventually flowed to 3 exits after, say, 60% of your liquid poured out you would achieve a much higher score than if you simply found the low point on the edge of the board. I suppose that could have been more explicit in some way.
As for logic and dynamic features a game might include I just never made it far enough for those additions.