Revision surgery for one implant that hasn't dropped after 6 months?

I certainly agree with your PS in that after 6 months it's unlikely that the implant will drop further. Without the benefit of examining you or at least photos, it's impossible to answer your question accurately. However, if a simple release of the lower part of your implant is necessary, a local anesthetic may be effective. If you have a capsule formation, I expect it would take removal of the capsule as well as lowering the pocket for the implant. If this is the case, a general anesthetic is necessary as this is much more involved. Your plastic surgeon is in the best position to answer answer your question, and what he suggests certainly sounds reasonable.
Thank you for your question, and good luck.

Dear Res,  It is difficult to answer your question without seeing your front  picture or examining you.      If the problem can be solve by inferior capsulotomy (scar release) alone, than sedation anesthesia , most likely is sufficient. However, from your description of one  breast being 'noticeably higher', it might be a case of 'Biofilm' that require capsulectomy ( scar excision) and implant replacement. In that situation , general anesthesia with LMA  is required.   As long as your surgeon is experienced board certified plastic surgeon who operate in accredited surgery center, most likely his recommendation to you is the correct one.    Sorry for not being more helpful ,                                                    Best of luck,                                                                         Dr Widder