5 1/2 weeks post op saline 600cc mentor implants under muscle, concern that they are riding too high. Does this look normal?

Congratulations on your recent surgery.  600 cc implants are large and will take some time for your body tissues to relax and allow them to settle lower.  Massaging continuously and going braless are all helpful in assisting your body muscles to stretch and implants to descend.  Keep following your plastic surgeons recommendations. 

It is far too early to be concerned. You very large implants and it takes longer for the implants to stretch the tissues and drop. Wait at least 6 months before even thinking about the need for revision.

Thanks for the question and the photos. The implants are in a high position. When I place implants in a sub muscular position, I keep them too high in anticipation that they will drop over the first few months. Be patient. You are only 5 weeks out. They will be in a better position within the next few months.