Better Termostate - Use Group as Window sensor fails

Hi, i´m using Better thermostate and have a room with two windows, each equipped with a zigbee sensor. So i´ve created a group of these two window sensors that report an “On” when one window is open (all entitites disabled).
Suddenly thats the opposite of what BT expects. How can I change that expectation in BT, so it stops heating when Window=“On”?