multiple closest points or magnetic field?

Dear All,

I'm trying to change a variable (radius of circle used as an example) at multiple points of a regular grid, based on their proximity to multiple objects.

I have tried to define the radii using 1. the distance to their respective closest points and 2. the strength of a field at the regular grid points when the origins of the objects are given a charge.

I thought the problem was referencing the lists correctly against one another and I have tried to graft the branches at various places in the definition (I am not sure where the correct place to graft is) and to sort the lists using each other as a key (My attempts to use a pathmapper were also unsuccessful).

These two problematic options are grouped in red.  The rest of the definition seems to be working ok.

What is the best of the two methods to use and how can I solve it?

Cheers,

Brian