Moving brep along curve porportionally + flipping curve lengths on z axis

Hi! I am very new to grasshopper so please excuse me if I have refer to commands and actions incorrectly.

Goal: use spheres to Boolean from closed surface with a gradient of how deep the Boolean cut is on the surface. The surface is cone shaped.

To do this I have created spheres with a gradient in their size ranging from smaller at the top of the cone to larger at the base, see below. I'd like to move the spheres along the curves which I have drawn from their centre point to a central point on a (z axis) line in the middle of the cone. I think I have managed to achieve this, however I would like to flip the lengths of the curves on the z axis. That way I can adjust the spheres to penetrate the surface at the top of the cone whilst barely touching the inner side of the cone.

I would really appreciate any input on how one may do this!!