Further explanation may be provided by analysing the contributions to the sub-gap excitonic transitions, as shown by a projection of the contributions to the 2.59 eV excitonic wavefunction back onto the quasiparticle band structure, as shown in Figure . The exciton demonstrates a hybrid behaviour between Wannier-Mott and Frenkel behaviour. As expected, contribution from the valence and conduction band arises from all kpoints across Γ and Z, consistent with complete localisation in that direction and thus a 2D exciton; along the other directions from Γ, there are however still significant contributions from multiple k-points, despite the low effective masses of both electrons and holes in that direction. Most notably, in the valence band, there is additional contribution from the band below ('VB-1') where it crosses the highest energy band, particularly along Γ to X: this mixing may explain why the exciton transitions are further partially allowed as detailed above.