To be clear, I'm not making excuses, I'm giving explanations.
X-Plane looks at the geometry of an object (fuselage, cockpit, windows) and determines how to bring light in. This is not something WE control.
A stationair has high wings. I would expect things to be shaded a bit better, as sun angles can't get through the high wing to the window as easily, so I suppose that makes sense. Additionally, I do believe that G1000 is part of their custom, old XP10 coding, which was not optimized for X-Plane's rendering engine in v11.
Nature of the beast. We can take a look, but on this one we can't make promises. X-Plane can be a little too smart.