Calculation of focus points for DC


Workbench the lateral focus point used in the pseudo section is calculated as a weighted average of the midpoints of all electrodes in the measurement, each midpoint is weighted with the distance between the two electrodes defining the midpoint, for a four electrode measurement there are 6 midpoints, the calculation is as follows:

As it is seen, the midpoints where the electrodes are close to each other are weighted heavier than if they are far from each other, this is what causes the lopsidedness in your pseudo section. 

This formula has been derived empirically by calculation the 2D sensitivity for 100’s of realizations of different electrode configurations. 
This lateral focus point only has an influence for the plotting and dont have any influence for the 2D inversions. IT has though influence for the 1D inversions.