Placement of Electrodes for Electrochemistry?
It really depends on the process and how 
homogeneous electric filed is needed. The more are electrodes close together, the inhomogeneity will be greater. 

The second problem will be with the homogenity of the solution. You can assume, that electrolyte is kinda homogeneous in a bulk. But more close you get to the electrode, the more is the electrolyte separated. 

Ions, as a charged particles, are transferred to near electrode surface.