curves's vertical attraction-wooly paths

Hi everybody!

I'm using the Daniel Piker's definition with kangaroo.

At first I used it for a 2D curves system but now I'm tryng with a 3D system.

I would make the curves attract themselves, but vertically only on the axis z.

How can I do it?

I created a curves system in the space, the curves move also in the same plane, I don't want it.

I tryed also to set curves on curves previously deformed (gh2 file), but nothing happens, I don't understand why.

Basically I would like : firstly that the curves attract on the same plane; secondly the curves, just deformed, attract only vertically.

I hope I've explained it clearly.

Thank you so much!

Laura