I have been driving a 2015 Model S (AP1 I think) while my Model 3 was getting some work done. I noticed that it had a two-stop sensitivity setting on the stalk.
Since the M3 is completely digital, it wouldn't seem like a terribly complex thing to add a multi-step sensitivity setting for those of us that are ok with some buildup before activating and those like my wife who goes nuts if there is virtually any moisture on the windshield (thank God for separate temp settings =). I think I'll add that as a 'note' or 'bug report' when I get mine back.