You can use index matching fluid to determine what the nylon line is currently at and then use the fluid to experiment with epoxy droplets containing various amounts of low index additives like MgF2 nanoparticles or something :)

The rabbit hole never ends. Godspeed, friend.

Add a polarization filter coating to the epoxy? https://en.wikipedia.org/wiki/Optical_filter#Polarizer

Also, if the plastic can be "invisible", you can also house it in invisible plastic- thus creating, a exploded working model, inside the resin

The author mentions this, a cylinder shape causes a lot of optical deformation so it doesn't look as good.