Thank you for your question.Although the size of the breast should not be different between an implant under the muscle and over the muscle, there are ways the size and shape may appear different.While the muscle is gradually descending, it is possible for the breast size to appear different because the implant will not be directly behind the breast tissue compared to above the muscle placement. Once the implant fully drops down, there should be no differences in size as the implant will be behind the breast tissue in both cases.Nevertheless, it is possible for there to be differences in shape of the breast when the implant is placed behind the muscle compared to above the muscle.When the implant is placed above the muscle (i.e., subglandular - directly behind the breast tissue), the implant can directly apply pressure on breast tissue to shape the breasts. This can allow the upper and inner breast areas to be filled more adequately. In fact, cleavage gap can be controlled more effectively. However, there are draw backs to above the muscle implant placement:Direct pressure on the breast tissue from large or high projecting implants may cause breast tissue wasting overtimeImplant may interfere with breast imaging and mammographyThere is often insufficient soft tissue coverage in the upper and inner sides of the breast and often fails to provide a natural superior poleImplant is exposed to endogenous bacteria in the breast tissue, resulting in higher rates of capsular contracture (the main reason why today most surgeons place their implants under the muscle)There are higher reoperation ratesThere is greater risk of symmastia (i.e., disappearance of cleavage) when cleavage gap is reduced too much and it can be difficult to correctPlease note that as a candidate for breast augmentation, subglandular implant placement may not even be an option if you do not have more than 2 centimeters of soft-tissue in the upper pole of the breast.These are reasons why the behind the muscle implant placement is the more preferred approach to maximize long-term soft-tissue coverage in breast augmentation.Hope this helps.