Tetrathiotetracene-iodide organic crystal (TTT2I3) is a nanostructured bulk material with pronounced quasi-one-dimensionality and with more diverse and complicated interactions. Mainly, the thermoelectric properties are improved by the partial compensation of two electron-phonon interaction mechanisms and the relaxation time has a Lorentzian behavior as function of Fermi energy. Initial predictions were made in the frame of a more simplified one-dimensional (1D) physical model, when the relaxation time maximum was limited only by the scattering on impurities, neglecting the weak interaction between the nearest conductive chains. However, more detailed investigations have shown that for ultrapure crystals the scattering on adjacent molecular chains becomes significant and should be considered. In this paper, a more realistic 3D physical model is presented. Also, the criteria of applicability of the simplified 1D model are estimated.