"In front of the chest" is just how I describe the mental model of maintaining a large triangle between the clubhead, my arms and across my shoulders. Sometimes I get a bit anxious and fold the arms back too soon, giving up width and club speed, and usually ending up coming over on the downswing. Once the club gets back to about level, the left arm begins coming across my chest naturally.

I don't know if that is necessarily a good image, but that is what I try to think of on practice swings.