For those attempting to replicate the same visual effect, make sure to use some extra thickness in between the front PCB and the LEDs. In this case I used 2 pieces of 1.6mm PCB stacked, 1.6mm should have been enough, but by adding more room you get some more space for the light to evenly distribute. For the front PCB, use copper on the top layer, this will allow the FR-4 to first diffuse the light and gives you the sharpest image. A previous test with 2020 WS2812b LEDs resulted in not such a good result due to the lower light output of those LEDs.