The effects of Ti–6Al–4V part size on its temperature distribution during the blown-powder directed energy deposition (DED) process were investigated through dual-thermographic monitoring and a unique modeling technique. Results demonstrate that the duration of dwell times presented to be a significant contributing factor affecting the rate at which a steady-state temperature field is achieved. Longer thin walls took significantly more layers/time to achieve a uniform temperature profile. Maximum and average melt pool temperatures appear to be near independent of part size at steady-state. Finite element simulation results showed that a quasi-steady melt pool temperature may be unique to a layer, especially during earlier cladding processes near the substrate and that the layer-wise steady melt pool was achieved within the first few seconds of track scanning. A proposed fin modeling-based temperature distribution was found to predict the thermal profile in a “substrate affected zone” (SAZ) along the scan direction within 5%. A method to predict the onset of the SAZ has also been proposed. This work demonstrates that process parameters used for the DED of component volumes are not necessarily optimal for thin-walled structures due to variation in thermal capacity.