320cc moderate low & breast asymmetry, how to best correct? (Photos)

I am very concerned about the size and high riding position of my left breast implant and am contemplating a revision. The deformity is causing the appearance of a droopy left breast versus the right and an obvious nipple height asymmetry. The fold position seemed symmetrical pre-op, but the left fold post-op is approximately 2cm higher than the right. What are the possible causes of this, and the possible treatment options to ensure a symmetrical result. The implants are 320cc moderate low.