You give me good and cogent scientfic reason but i didn't say isolate part of muscle
My idea in make more percentage of intensity in apart than another
Muscles are stupid. They don't work by percentages. When the nervous system notices a stress or force being put upon them, or given a task to do something, they recruit the muscle by contracting as many muscle cells as needed to create a needed reaction or produce the task given. Lats still consist on mainly one specific part. It all come to a single insertion. I understand the confusion, so lets look at the quadriceps femoris. That's a muscle that can contract more on certain parts than another. But that is because it originates from four different points and theses parts insert to a common tendon, a fibrous tissue. So basically there are plenty of angles to pull, right? With the lats, all the origos are to form a single muscle, a single head. Not four, but one. So there is no difference in activation of the origos.
I'm still very sure that these youtube trainers and pdf's are talking about the relationship with TERES MAJOR and Latissmus dorsi. Unless you can show the sources you talk of, there's no reason to go further.