It is indeed very uneven, had similar issue even after two try.
For anyone that is looking for a good, cheap, light source with very high CRI and brightness + evenness, I recommend RaLeno PLV-S192:
If you look at the Duv value, it has almost perfect score (the light is perfectly WHITE with no sign of green or purple, read more here)
Although NS 4x5 uses a better LED strip where R9 and R12 might be slightly better, the unevenness is a true problem. Plus the brightness is also terrible. I DO NOT recommend spending 300 dollar on them (it’s Waveform Absolute Series, which only cost around 10-20 bucks for the two strips that NS used in its 4x5 light source).
Get PLV-192 and all your problems will be gone! (After calibration I use the light source at around 4700K → which measured around 5000K).