It seems that Apple uses kCACornerCurveContinuous for smoothing the corners of the screen, since there is a noticeable visual difference between the normal notch and this tweak. Here's how to fix it; I will make a PR that includes a fix. I don't have theos set up, so I can't test if it works.
When starting the camera from the lock screen, there is a black line on the left side of the screen, the startup from the control center and camera application is normal
On my iPhone X, the radius is slightly off. For one, it doesn‘t blend smoothly with the sides of the screen, see attached screenshot:
Edit: It‘s really hard to tell on that screenshot. Either this is due to the white background on GitHub or the iPhone slightly clips the screen.
Also, the radius appears to be slightly smaller than the lower corners. This doesn’t show on screenshots, unfortunately.