Manage brush size with wacom: how avoid irritating pop-up brush menu?

I have been using the wacom tablet for years to manage my brush size and harshness on the fly with the lower button of the pen. Recently, I have uprgaded to the new Wacom Intuos pro. After installing the same pen-settings, there is quite an annoying problem. When using the pen for enlarging or decreasing the brush size, it doesn't do the job but instead lets the fly-out menu of brush settings pop up the screen. After trying multiple times the normal function takes the winning hand again. But this is irritating, as it slows down my workflow considerably.

I have been looking for a solution on the internet, but have found none. Anyone any idea??

Thanks in advance! Rob