The surgeons usually make the decision based on how much natural breast tissue you currently have – as under muscle when you already have quite a lot of natural boob can lead to double bubble just as over the muscle with no natural boob would look really fake. You need to have a proper chat with your surgeon about what you want to achieve and how he proposes doing it…see a few different surgeons to get a few opinions then go with the one you’re most happy with. There’s lots of potential pros and cons to both options so don’t listen to anyone who tells u that one or the other is crap and not to go for it – because it’s all dependant on what’s best for the individual xx