Intimacy with the lens in the case of the single model is intimacy with the viewer, but with two or more models working together to creat a senual storyline, they should only be focused on each other. In these cases, when one or more of them look deeply into the lens, it breaks the spell.

You are correct that the dynamic changes with more than one model.  I would observe, however, that even when only one woman is in the shot, she doesn't necessarily have to be looking directly at the lens.