5'5", 120lb, 2 years post-op, under muscle & have placement concerns (Photos)

5'5", 120 lb, 2 yrs post-op, under muscle. Laying down, my left implant shifts towards my armpit. Any minor left arm movements would causes an indent on the center of my chest. The implant looks better when I'm up right and arm is completely relaxed but you can still see the indent. I've spoken to my surgeon and he said I didn't have enough fat on the left side of my chest. That doesn't explain the implant's shift, single spot indent, and perfect appearance when I'm up right with relaxed arm.