How to resize ofxFaceTracker

Sorry for a beginner question but I’m trying to adapt example-expression from for my app. In particular, I want to make the tracker fullscreen. In order not to re-initiate the grabber I’m using:

grabber.draw(0,0, ofGetWidth(), ofGetHeight());

but this results in the tracker being drawn out of the alignment, in the original position.

How can I resize the ofxFaceTracker tracker to fit the size of the window and remain aligned?

Thanks in advance, zb