For the Qolsys panel, the sensor group programming field for each zone determines how the sensor reports are handled in different arming states.
You can edit that sensor in programming (Settings > Advanced Settings > Installer Code > Installation > Security Sensors > Edit Sensor) and use Sensor Group 15 for that motion detector, which is a motion sensor group which will alarm on Stay or Away.
See the thread below for a description of various sensor group options.