Are the front and back lengths of the baldric the same? Is the baldric simply a length of cloth/leather?
You can define where the highpoint of the curve is by putting a dart into the baldric on the shoulder point. It won't want to rotate at that point. To put a dart in, you would fold over part of the baldric material on the neck side, but not on the shoulder side. If it's cloth, you just make a triangular tuck and sew it down. If it's leather, I would cut a slice in the baldric from neck to shoulder and then pivot the cut edges so they barely cross each other at the shoulder, but one lies on the other about an inch deep on the neck side. Then I would stitch that new triangle/diamond shape down a lot since it's going to take the strain of the whole baldric on that join.
Ideally, you would have a helper to measure you from sword-hip across your chest to your shoulder and down your back to your sword hip again. Then compare the two lengths. I would imagine the front of your baldric needs to be shorter than the back of your baldric, but everyone's body is different.
Hopefully, if my advice is bad, someone will come along and offer you a dissenting view. I just know that when I wove what amounts to a pageant sash, I had to sew that shoulder tuck to get it to lie flat on my shoulder and not move around. Admittedly, it wasn't bearing any weight, but that's why I offer the advice I do.