Whatever Epicurus thought about the theory, he was dealing with the exact same facts and human nature that we are dealing with today, so he would not have had facts which are not available to us to flesh out the theory any more than we can today.
Point taken on human nature, but we do have access to additional facts on the workings of the human body at a much finer level detail (down to the molecular and atomic level) than any ancient person had access to.