Help to figure out xinput transform matrix for a tablet?

I have a small wacom pad and a large monitor. And i wanted to reduce the area of the screen where the tablet surface is mapped. Sadly graphical utility does not allow this. Currently the configuration is the following: Coordinate Transformation Matrix (216): 0.571429, 0.000000, 0.428571, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000 This maps to the HDMI connected 2nd monitor in landscape mode. I want to rotate mapping 90 degrees and use half of the screen in portrait mode. Infotunnely just multiplying given figures to rotation matrix gives total mess. As i unerstand due to not square shape of the area. But no idea how to do it right. So basically i need do the following.