I've just got an old Aiptek-compatible graphics tablet (304mm × 228mm) to work with my lenovo X220 ThinkPad with an additional external screen.

The primary display is the 13" built-in screen with a resolution of 1366 × 768 (16:9).
The secondary display is an Asus 24" screen with a resolution of 1920 × 1200 (16:10).

The arrangement of the combined displays is such that the primary is below the secondary, and centred with it.
Screenshot from 2020-11-17 17-41-14.png

The surface of the graphics tablet currently represents the total surface of the two screens, so that placing the pen in the top left-hand corner of the tablet moves the mouse pointer to the top left-hand corner of the secondary screen and placing the pen in the top right-hand corner of the tablet moves the mouse pointer to the top right-hand corner of the secondary screen.

However, placing the pen on the bottom edge of the tablet and about 35mm in from the left-hand edge of the tablet moves the mouse pointer to the bottom left-hand corner of the secondary screen, and similarly placing the pen on the bottom edge of the tablet and about 35mm in from the right-hand edge of the tablet moves the mouse pointer to the bottom right-hand corner of the secondary screen.

The result is that when I try to draw in gimp with the canvas on the secondary screen, the left to right movement of the pen corresponds well to the left to right movement of the pointer, but up and down movement of the pen, covering both screens, is not registered with the movement of the pointer.

Is there some way to configure the system so that the tablet's surface represents only the secondary screen?