I would probably say that it was in use from when I start to read it until I finish, or possibly when I acknowledge to myself that I’m not going to finish any time soon.
Suppose I read chapters 1-27 of a 30 chapter book and set it down on the coffee table to make dinner. My husband picked it up and put it in his suitcase to take on his next work trip.
I would not be happy about that (and would ask him to put it back if I realized before he left) on the grounds that I wasn’t finished with it.
Even by your definition, my reading is not restricted to a single location. I mentioned the sofa, the comfy chair, the bed, the chair in the waiting room at the doctor’s office, and the chair in the exam room at the doctor’s office…
And within those locations it’s not really stationary either. I’ll shift positions, cross or uncross my legs which changes the height of the book, switch hands, etc.