Whether the clubshaft plane angle gets steeper, more shallow or stays the same after impact depends on what you do with your PP's pressure through impact and beyond. I think.
My contention without being contentious, is that the Pulley System describes what Plane is being used for the start and the exit.
Is that like saying "rain is wet?" If it is, I'm sorry.
I'm trying to be technical and, well, it's not a naturally given skill.
ICT
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HP, grant me the serenity to accept what I cannot change, the courage to change what I can, and the wisdom to know the difference. Progress and not perfection is the goal every day!