Randomize Heights of Building Extrusions

I have used the Elk plugin to create 2d shapes of buildings for an area. I have imported that OSM data. None of the buildings in this area contain levels or height info, so my plan is to extrude them up at random heights within a range, so they aren’t all the same height. I can successfully extrude them but am having trouble getting random heights. What I have now extrudes every cube the number of variations I have set. So I have set a random number in a range with 5 variations, but the buildings are all extruding at those random heights 5 times. I followed some videos online to do this, and I believe I have it set up the same way, but I am still getting these duplicates. Can anyone point me in the right direction?

GRAFT the Z vector to match data

Ah, thank you!