Shape tween - Height of the shape

Hi, 

I'm working on an animation that involves some hydraulics (water level rising). 

My problem is that when I change the height of the rectangle that symbolises water, Animate starts changing the height by adding it to the bottom of the shape.

But for me, as I'm working with water, it would have been much more conveniet if Animate would add height at the top of the shape.

Is that possible?