I'm 5'9" and I have a purple plum jumbo. It works for my height but the strap slips off easier and it's a lot heavier than the medium/large. (I also have spinal issues, fusions, etc.)
For the petite woman, the large bags are not in proportion to the person, but that's my opinion. If you love your bag and don't feel it's too large, who am I to say. But if you try the bag and think it's too big on you, then most likely it is and you are not going to shake that opinion. Get a full length mirror, wrap around mirror and see what you think trying on the medium and the jumbo.
For the petite woman, the large bags are not in proportion to the person, but that's my opinion. If you love your bag and don't feel it's too large, who am I to say. But if you try the bag and think it's too big on you, then most likely it is and you are not going to shake that opinion. Get a full length mirror, wrap around mirror and see what you think trying on the medium and the jumbo.