Move/copy objects in Z and scale parabolically with 0 as base plane

I am trying to create a boulder definition using curves drawn in Rhino as a basis.

My aim is for the curve in (Rhino drawn at '0' Z direction) to represent a boulder footprint on the ground plane. Ideally, half of moved/copied curves in a series (or similar?) would move in positive Z direction (above 'ground') and half would move in negative Z direction (below ground).

I am using the scalar component as well to essentially make a stack of concentric curves I can loft. I want the scalar relationship of these curves to be slightly random but more or less parabolic on a whole - largest curve in middle, smallest curves at top and bottom.

Please see diagram, and 3dm gh files...

Any feedback/advice would be sincerely appreciated...

Thanks,

John