In my experience this has always required prototyping. We just finished a project that had an LED edge lit effect with several LEDs hidden around the perimeter of a translucent part with some laser etched details to dissipate light. The only way that we found to get it to work was to make several prototypes. The clear part is compound curved so we first tested it with flat parts. Then we laser etched and drape formed a test part to try out LED placements, then made a full prototype.
If anyone else has a better way, I’d love to know too!