The landenburger spinnaker shape is getting flatter and flatter. How far are we off dropping the loose luff all together and just sailing with a hard luff? Reacher, screecher, hooter (or whatever you want to call it)

What is the purpose of the Gennaker girth rule?
The gennaker girth rule : at least 75 % of foot length (SF) at midheight (SMG)

Is it to prevent the sails from being used up wind?