Good to see you are determined to get your head round this !
So hopefully to help
a) As said all parts will flex/ compress / give a little, if this was not the case as soon as the pads touched the disks there would be no more pedal movement be it gentle braking or emergency stop, clearly the peddle does move proportionally to brake effort so it is normal even within it working range.
b) Connect scanner to ABS and graph brake pressure, monitor pressure while applying brake. You will find that if you maintain constant fluid pressure no creep will be felt And when pedal creeps pressure will increase.
This has been noticeable on many systems for a good few years now, some more noticeable than others, I assume you are not an MOT tester or you would have come across it before.
I suspect they use these high vacuum systems so increase number of reserve assisted applications of the brake if engine stops or if driver applies & releases brake in quick succession. You may remember in the good old days when it was common to have a remote vac tank for extra storage, not needed with these systems.
Aidan
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