Loss over distance calculations appear to be per device. In my testing:
- Solar Panels (1EU/t) have 0 loss if they travel 9 blocks of Tin Cable or less, and 100% loss for any longer distance.
- Bat Boxes incur a loss of (3/40000)+(cable length)*0.2 for both Tin and Copper (insulated) cables. I don't know the origin of the 3/40000 other than to note that a fully charged batbox will ALWAYS lose 3 EU plus any other computed losses.