I was asked recently about back carries with a mei tai. High back carries are good for smaller babies once you adventure into the world of back carrying (they need great head and neck control at minimum) and it great for when you don't want to tie the waist knot at your belly (upset stomach, pregnancy, etc). Aiden likes it because he can see over my shoulder.
High Back Carry
I tied the waist knot just below my boobs. When Aiden was smaller I would sometimes tie it above my boobs!
And to compare, here's a picture of back carry with the waist straps tied at my waist:
I didn't do it this time, but it is possible to tie a chest belt for many people when doing a high back carry, which helps some people back carry for longer. If you're having issues with being comfortable with back carries, chest bests often help.
One version of a chest belt:
Another version of a chest belt (sometime called 'tibetan'):
You can also buy separate piece best belts or steal one from a SSC (soft sided carrier).