How can I realize / test how much breast tissue is mine when I have breast implants?

It is easy to pull the breast tissue forward off the implants with your fingers. I have no idea what "puff" means. Lungs puff, not breasts. If you are talking of reshaping the breasts with a lift procedure, then yes it is possible but should not be done for 3 months after implant removal as the tissues will reshape significantly in that time.

I can usually give a pretty good guess of how much breast tissue a patient has when I examine them.  If you know the volume of your implants, it makes this task even more accurate.  I select an implant sizer the volume of your current breast, subtract the volume of your implant and show you an implant that is about your "real breast" size.  Removal of implant often results in sagging of the breasts.  This can almost always be treated at the time on implant removal with a breast lift.