Need to make variable height split screen effect or generator

I am looking for either an effect or generator with two drop zones that I can vary the height of the drop zones by dragging the line between the two zones. If you have used Disk Utility and created variable size partitions, the visual part of doing that is what I want to do. What I want to do is vary the space that is needed. Say I have some bullet points and they do not take up the whole space I want to make the lower zone taller in height to take up the unused space in the top zone. I am being clear enough in what I am wanting? I could make this in Motion but have not been able to figure out how this can be accomplished.

I figured out how to make this generator.

How? Link parameter behavior?