Motion Detection zone doesn't fill screen

I have a stickup cam protecting my campervan. The default motion detection zone doesn't cover the whole of the visible live view screen as can be seen in this combined screenshot. Is there any way of extending that zone vertically?The top view is the live view, and the bottom view is the extent I can edit the motion detection zone. The photo has not been cropped, that's a screenshot of the extent on my editing area, and I can't drag the zone any higher.