Trying to bind my wacom touch wheel to grease pencil brush radius (2.81)

in order to do that, i need two input in the wacom property editor, one for increase and one for decrease;
problem is, in the blender keymap option i’ve got only one input for the radial control (f key) and increase or decrease is obtained by moving mouse left or right.
i can’t really figure out which path property to type in order to have two scalar value, since i don’t know much about python and programming in general.
so, that’s pretty much it guys, thanks in advance for your time