A boat sails in the wind she sees.
Take away the windward boat from the picture and the boat still sees a velocity header.
Her proper course of action is to react to it.
And who can prove which boat is causing the blanketing, i.e., the overlapped windward boat or a third boat astern.
It makes no sense to allow a course change from a third boat's impact, which the windward boat might not anticipate, yet not allow a course change that the windward boat precipitates and expects.

Anders, it’s based on the perpendicular projected area concept of the pre-start and course-side of the line not including the extensions. 

The green line is the boundary on the prestart side between the starting-line and it’s extension. 

A  couple of things
1. There is no proper course before the start so 17 does not apply
2 . After the start if the overlap was established from astern  (back door) 17 does apply and L cannot sail above proper course.
3. If L was luffing to clear the pin end of the line that is their proper course, but once clearing the pin they need to come to a close hauled course 
4. If 17 does not apply then L can luff head to wind. If they go past head to wind they have tacked and broken the rule. 
5.  When L subsequently bears off if they overrotate to do so and there is contact it is all on L.  If they bear away and do not overrotate then W was not keeping clear. If there was no contact in that situation no foul

Any coach who coaches his team to intentionally break a Rule and then take a penalty for the purpose of gaining an advantage, has lost the plot.  In the unrealistic scenarios provided, any competent windward boat keeping a tight lock on their leeward opponent should still be able to easily maintain control of their opponent after the leeward boat had competed their 'voluntary' penalty.

Agree with all those comments which follow the principles of prompt decisions in team racing to avoid delays.
This is how I have handled it on the many occasions I have seen it happen:
- after the boat finishes, display the black flag to the competitor
- go to the competitor, explain that you have seen them go the wrong side of the mark and that you are protesting them.  Then state: "This is your hearing".  This provides the competitor the opportunity consider what happened and to provide evidence otherwise.  After discussion, I have always found the competitor to understand that they got it wrong.  The result of the hearing is then communicated to the RC.