As long as the dart isn’t interfering with the armsceye, it shouldn’t matter where it falls.
But this is an excellent video on darts and dart manipulation, if you wanted to adjust it so it’s more horizontal.
I echo Jonathan’s comment on the shoulders looking too narrow too. That could just be a result of a large bust on a narrow frame.
Sorry, I am not an expert on darts, with most of my knowledge of them from that The Closet Historian video that is posted above. From that video, my understanding is that darts can be located anywhere, along any seam, according to the preferences of the pattern designer. You would have to look at different patterns to see if there is a favored/standard position for the bust dart.
My main advice would be to double-check all your measurements to make sure they are correct. It seems that your issues may be due to incorrect measurements.
If you are just changing measurement values based on what the resulting pattern looks like, instead of changing the measurements to be correct, it is likely that you’ll get a pattern that produces a garment that doesn’t fit you.
I’m not sure what you mean by usually but it’s there because that’s where I designed it to be by default. As high as possible in the side seam, without influencing the arm hole.
That being said, this is Breanna. It has an absolutely ridiculous amount of places where you can put the darts. Look at the Bust Dart and Secondary Bust Dart options in the Style section of the Design Options.