As the first couple of months pass, the pectoralis muscle will begin to relax to accommodate the new implants. Until then, the pressure the muscles exert on the implant displaces the fluid (saline or silicone) upward to bulge in the upper breast, and incompletely fill the lower breast.
The implant is seated in a pocket the bottom of which is stable, much like the bottom of an envelope. The upper part of the pocket is a large empty space that reaches up to the collar bone, so that the pressure on the implant displaces the fluid to the area of least resistance.
This abnormal positioning is self-correcting as the muscles relax allowing the implants to "drop"
All the best.