Capacitance among N conductors
It has been a loong time since I did basic electricity and fields.

The simplest representation of a capacitor is two flat electric plate at a distance. There will be an electric field between these plates:
    

The electric field starts at potential V and, with a constant dielectric, will linear with distance go to 0V (Gnd). This means that in the middle you find a potential of V/2. 

If we place a very thin electric plate at 1/3d from V, the potential of the plate will then be 2/3V:



If you would externally set a potential of 2/3 V on that plate the electric field, and thus the capacitance would be the same.

This means that all your wires in the middle do not make a difference and can be ignored.




  But to solve the capacitance network you don't really need to know all these details right? 


As you can see, the voltage on those line places a crucial role.