I think that you underestimate the growth potential of string implants. Here's a pic taken just 2 weeks after I first got my string boobs put in. You can see from my shiny stretched breast skin, though, that BIG things were destined to happen soon. But neither Dr. Johnson or I had any idea just how big, or just how soon ! The second pic was taken about 1 year later ! Notice where my elbow is in relation to my boobs in the two pics - it will give you a fixed point of reference for the relative boob growth.
The outrageous growth potential of string implants which was quickly discovered was the main reason that string implants were pulled from the market. Even girls that went in for D cups wound up being a D cup for maybe a month, a DD cup a month later, and a G cup 6 months after that !!! This is great for a big boobs model, but not so great for a secretary, schoolteacher, etc.