Understanding the progenitor systems of Type Ia supernovae remains an open problem in supernova research. Thanks to theoretical developments in the last decade, we now have a variety of 3D hydrodynamic explosion models for various scenarios. These can be tested with nucleosynthesis and radiative transfer simulations to compare to observations. However, comparisons at early epochs have not been sufficient to effectively discriminate between scenarios. I will report on ongoing work to improve the physics of the ARTIS radiation transport code, in particular to extend its validity to later epochs for application to existing 3D explosion models. I will talk about the status of this work and present preliminary results from a selection of models.