I think there is a miscommunication here; when I refer to bobbing and weaving I do not mean head movement, per se, though that is in fact the bobbing part. I am of the opinion that the movement should not be a random hope he misses thing, but rather a deliberate move to avoid a specific punch. Call it slipping because when you slip you can punch and when you bounce your head like a ball you get off balance and can't.
Weavingis the key element here. It is moving the body in out and around the straight lead to create openings to punch. You may begin by slipping to the outside position be dropping wt tort foot; as jab passes by lean slightlym forward while stepping in and left w/left foot, bend trunk slightly and move head to left under his lead and up to basic stance position. You can slip the left to the inside,bend slightly forward move head to right under opponents arm and up to position