[Request] How accurate is this?(i.redd.it)

Did you integrate this numerically, or maybe there a table where one can find common fits for form factors?

I integrated numerically. The integrand is the inverse of the square of the distance from the observer to any point of the cube.

Integrate [(x^{2} +(y+d) ^{2} + z^{2)} ^{-1} , {x,-L/2,L},{y,0,L},,{z,0,L}]

Corresponds to an observer at a distance d of a cube of side L. The observer sits on the floor in the center of one of the sides of the cube