Probing the origin of variation in the λ(uNi) region through SYNAPPS model comparisons. The top panel compares SN2011fe and SNF20080514-002 at an early phase (−10 days). The second panel repeats the early SN2011fe spectrum (blue line) together with the best SYNAPPSfit (black dashed line). The green line shows the same fit, but with the optical depth (τ) of all Ni and Co II decreased by 1 dex, effectively suppressing these ions. The third panel compares the early SNF20080514-002 spectrum with the same SN2011fe SYNAPPS fits. The SN2011fe fit with suppressed Ni; Co II optical depth matches the SNF20080514-002 λ(uNi) region well. Vertical dotted lines indicate the U-band spectral index boundaries, with λ(uNi) lightly shaded gray.