Severe parallax using Sidecar / Screen Mirroring / Airplay on iPad Pro with Macbook Pro

Exactly - this is as if the screen is an inch thick and is causing a difference in pen position and actual cursor position. If I draw a dot in the middle of the screen it is perfect; If I draw a line from there it starts to become offset so by the time my pen is at the very top of the screen the cursor is only about 90% of the way there. Same top to bottom, left to right. It only moves about 90% of the distance my pen moves. This makes sense if the iPad is adding a touch bar at the side or bottom and isn't compensating for the reduced usable screen size compared to the actual touch screen size, but turning this off has no effect.

Maybe this image will demonstrate how the drawn dot is offset from the tip of the pencil, by an amount relative to the distance from the centre...