The picture of Bragg's Law and that simple planar molecule in the Introduction certainly oversimplifies the situation: in general, the electron densities in the unit cell are not concentrated in parallel planes. A more realistic depiction would have atoms dispersed at various locations in between those planes:

in which the resultant reflection recorded on the detector is the sum of all the individual atom diffractions. Upper case “F_hkl” is the resultant structure factor (the detector records the Intensity of the diffraction, which is proportional to F²); the lower case “f_j” is the scattering power of atom j in units of electrons. The exponential expression is the phase angle of the individual atom diffraction. This expression can be looked on as a correction to the phase angle necessitated by the atom being “out of” the Bragg plane (if atom j were in the top plane, the phase angle would be 0° ; if it were in the bottom plane, the phase angle would be 360°). The quantities x_j, y_j, z_j are the atom fractional coordinates along the a, b and c unit cell axes, respectively.