Just tried on multiple dresses for evening wedding. The knees need to be well covered. I am a leggy 5'8" and luckily found one that worked. Very hard to be happy with dress length. I also don't want to wear super long tunics regularly, especially in the heat. I am in a car too often to want to corral a lot of volume day to day. There are more longer options than there were about 5 years ago, though I like dresses just below the knee, not always midi.
Good luck to all of us. My almost 6 foot tall daughter struggles with dress length every shopping trip. Some midis would be a good length on her, but then the other proportions are off, of course.