Top-panel: Piro (2015) model (dashed lines) for the early light curve of iPTF15dtg, in Bgri-bands. This model describes the emission from a star surrounded by extended material and it has been constructed to reproduce double-peaked SNe. In the modeling, we adopt the ejecta mass and explosion energy derived from the hydrodynamical modeling. Shown by dotted lines is the Bgri emission from the ⁵⁶Ni contribution, as derived from the hydrodynamical modeling. The sum of the Piro (2015) model with the ⁵⁶Ni contribution provides a good match to the early peak, as well as to the rise to the main peak. This is due to the short timescale of the emission from the extended envelope. Bottom-panel: reduced χ² surface plot for the Piro (2015) model fit, given different values of R_ext and M_ext, for the explosion epoch derived from the best fit. The best R_ext and M_ext fit values are indicated by a white cross. There is a clear degeneracy in the model fit for R_ext ≳ 500 R_⊙, and M_ext ≳ 0.045.