How to get more smooth gain of brush?

I can’t properly vary smear thickness when applying different level of pressure to graphical tablet. I tried different “Gain” levels in brush settings and here is what I’m getting (from lowest to highest):

MyPaint 1.2.1 on Ubuntu.

My tablet is Genius G-Pen M609X.

Can you run gtk3-demo and observe the pressure when you run the tablet and drawing demo? I’m thinking this is Driver issue that I’ve seen before. Some devices have sudden swing in pressure. You can somewhat compensate for that with a global pressure mapping curve

Here it is (I had to press very hard to get thick line) (by the way ArtRage on Wine is fine):