AI Perception: howto change height

Probably a simple question but I can not find it. I can change the perception range & angle. But how do I change the height of the perception? It seems to be a fixed height but I can not find where it comes from and I can not find a setting for it anywhere. I’m sure I’m overlooking it.

In the image below you can see that the turret is not visible because it is placed too high. The vision range is 9000 and the vision angle is 180 (well actually set to 90 but effectively 180 due to a bug that is currently doubling the vision angle).