Tomatorit - Ficus carica is deciduous wherever temps fall close to or below freezing. The colder it gets, the more cold-related dieback there will be. I'm not sure I understand the distinction you are drawing between your two theories. The dieback occurs because of cold temps that start in early winter and continue through the winter.
In your area, the best practice would be to wrap your trees for protection as soon as temps start to get close to freezing in the late fall and leave them wrapped until sub-freezing temps are over in the spring.
