Dropping & fluffing
I do think implants do "settle and soften" which is what it appears you mean by "drop and fluff". This is related to the swelling of the pectoralis muscle and tightness of the skin envelope which resolves over a few weeks. The natural look of the implants takes several weeks and the soft feel may take a few months as the post operative healing takes time.
Breast implant surgery causes a lot of swelling that takes months to resolve. As the swelling resolves, it appears that the implants "drop", but they really don't drop, it is just the resolution of the swelling. I am not familiar with the term "fluffing" as it relates to implant surgery.