Line core formation of Hα, Ca II 8542, H&K, and Mg II h&k within the MPI-AMRVAC-simulated filament. The average formation height z_a calculated inclusive of the FAL-C chromospheric model for the line cores as previously shown in Fig. 8, overplotted on co-spatial distributions of the primitive quantity of temperature, and Hea15-inferred electron number density and ionisation degree.