V-tail mix for quadplane

Hi altogether, me trying to setup a quadplane with a v-tail. Autopilot is Pixhawk 1 (2.4.8) .
For the quadplane-part I managed to setup pitch, yaw, roll in the right manner. But v-tail-mix gives me either pitch or yaw reversed. Did I oversee a parameter which enables me to change one of these only for the v-tail mix?