A mun sau can be a punch...so maybe that is what @hunschuld is saying.
Yup!
How do you define punching range?
Once your range is reached, do you initially engage by stepping forward with a mun sau to create a bridge?
Technically 2 punching range issues however experience boils it down to one. The two are when can I hit him and when can he hit me. In essence when I am in a range that I can hit him with stepping in..
For example Lets say I am left side forward and think that I can step in and hit with a jab, pole punch for those about to scream WC doesn't have a jab, I am trying to hit but I expect he will block intercept because of the distance so I punch but am also asking for his hand. Since I have trained for this the instant contact is made I move on to what to do next.