The decision about implant size depends on many factors. The size of your chest, body type, base diameter of your breast, and skin quality all help to determine the "optimal" size for you. This size might be very different for another woman. There are also many ways to help you to determine what implant size would fit you well. Some plastic surgeons have "sizers" in their office that they will fit into different size bras so that you can begin to see what kind of a change you would get with different size implants.
Other ideas are for you to use water or rice in sandwich baggies in a bra of your choosing at home, and then try on different kind of clothing to determine what looks best. Sometimes, if a woman is having a very hard time deciding on size, I have her bring in the bra she would like to fit into after the surgery, we sterilize it and use it to size her in the operating room. In your case, you may be noticing a change in shape, more than a change in size.
I have had a number of patients swap out saline implants for gel and have the same impression that you have. Typically these are patients who loose some fullness in the upper part of their breast as the implant in replaced in a more "natural" position. Hope this information is helpful!
