Our design mentality went something like this:
1: We want to hang.
2: Its easier to reach a 7’ bar when you’re 5’ tall than when you’re only 18" tall.
3: Build a tall robot and climb the bumps.
Another thought to add.
The strategy I believe will work in regional competitions works best with one alliance partner who can move between the field’s zones. Not necessarily or always doing so, but at least one alliance partner needs to have the option. The only way to ensure an alliance always has a particular component is to put it on your own robot.
@ =Martin=Taylor= : It’s easier to fall over with a 5’ robot than it is to do so with an 18" robot. 
That’s a rather arbitrary statement. Just because a robot is tall doesn’t mean its COG is high.
The top part of the robot can be built very light.
I’f this game turns out to be like 2003, where the actual task is too difficult for most teams to accomplish (controlling and kicking the balls). I foresee low robots, with scoops scoring most of the balls by pushing them under the tunnels.
But I would be amazed to see an 18" robot with a center of gravity higher than 18".