I often get skeptical glances when I tell girls to gather the breast tissue into the bra from their back. I guess it does sound strange: how on earth can breasts escape that far?
Here is a rather extreme proof that breast tissue can migrate to the back if not given enough support / squashed by wrongly fitting bras:
Of course this example is rather extreme, but still many girls who have been wearing the wrong bra size for years have a bit of breast tissue at the back. And it's not necessarily the plus-sized ones either.