I think synergology sounds quite interesting. I've surely done less reading on the topic than you, but I have thought about it a lot in the past. I notice a difference in the amount of non verbal communication from person to person and culture to culture. It's interesting how some is virtually the same across the world, and others not at all.

I do a lot of non verbal communication, or combine it with verbal in various ways. I am not sure of the answer to your question, but my guess is that non verbal language includes gestures or physical non verbal expressions that we (and the recipients) know the exact meaning of through specific learning. We know someone in the same area will know what it means (like waving a certain way means "hello" or a middle finger is a nasty gesture meaning...) I think non verbal communication can include such language, but also physical expressions that are not done deliberately for communication sake, but perhaps beyond our control. For example, tears flowing may show sadness, pain, or even great happiness. Sweating may show anxiety, overwork, or many other things. Heavy breathing also many things. Situation context may be needed.

We may say one thing verbally, but our facial expressions show something else. The latter can be done deliberately or beyond our control. We may use two or more contradictory non verbal signs to mean something else (i.e. giving your sister the middle finger with a big smile on your face to be more of a tease, than angry gesture).

Communication is definitely a fascinating subject!