I’d need to know exactly which preset you are asking about to give a precise answer.
Certain presets use an additional phosphor layer for the screen that is affected by the ambient light. Like a real CRT, it effects the contrast in daylight.
When the phosphor layer is enabled there is also a shadow cast on the top of the screen from the surrounding bezel.
@HyperspaceMadness pulled out all the realism stops developing the Mega Bezel. Combined with a realistic screen reflection (Another optional image layer.) it gives the tube a photo realistic look.
Here is an example that also showcases the shader’s ability to auto scale to ultra wide displays.