It is possible that we do not have to account for 3D space using the factor , but must account for the fact that the single charge is a lump of particles. In any one direction half of these particles on one side shield the other half of the particles on the other side. In effect, a test charge only faces half of the total number of particles in a single charge. The effective number of particles, is,
half the total number of particles in a charge, .
So,
in any one direction.
Good night...
If we really fuss about it,
when the experiment to find the elementary charge is using repulsive force and the situation is presented with the least repulsive force.
Good morning!