On element tuning it says that when boost is not reach it goes to
PWM map4 load zone, Going from high load zone (100%) if boost is off target.
Each load zone is set by cycle duty on the boost controll.
My question is why would you not do a linear cycle duty proportional to load zone. 100 load = 100% cycle duty... 90 load = 90% cycle duty.. and so on.

Because boost is not "on" in every load zone (low load = no boost) and up to the wastegate cracking open their is no reason to control boost.

Do you want to adjust something, or are you just trying to understand the logic of boost control?