When the frequency of AC divided by the speed of light gets close to the length of your wire (ie. around 1Ghz), the regular rules of electricity no longer apply.
In the high frequency rules, you should consider that the energy you're sending down a wire is instead transmitted in the insulator - ie. it is effectively a radio wave guided by the conductors on either side.
If one of your conductors is not a wire but a ground plane, then the radio wave will travel in the insulator between the other wire and the closest bit of ground plane. Further away bits of ground plane, the signal gets effectively cancelled out because all the alternate paths the signal could take all have different path lengths and therefore phase shifts.
In the high frequency rules, you should consider that the energy you're sending down a wire is instead transmitted in the insulator - ie. it is effectively a radio wave guided by the conductors on either side.
If one of your conductors is not a wire but a ground plane, then the radio wave will travel in the insulator between the other wire and the closest bit of ground plane. Further away bits of ground plane, the signal gets effectively cancelled out because all the alternate paths the signal could take all have different path lengths and therefore phase shifts.