Space truss member size control (K2, Lunchbox)

I have built a space truss with lunchbox and trying to use Kangaroo2 to maintain the same member size while keeping a similar form. I am not sure about how to use the length component in Kangaroo, most tutorial I found online is teaching tensile structure, rarely they talk about the length control. and it become even more complicate when come to a 3d space truss instead of member on a single surface.

Space truss (23.6 KB)