On the first mock-up, I marked where the bottom of my breasts were. Then on the second mock-up I made the gussets go til there, and moved them to the sides, too, so that they were at the exact lowest part of my breasts. I cut out a size 8 instead of size 12 (mock-up #1 seemed ok on the size only because the space was filled bith my squished boobs), but I kept the straps in size 12, as I'm pretty long in the torso and I know my breasts are lower than most women's. I only had to make them narrower in the front - the side gusset ended up almost in the middle of where the strap originally was. Mmmh, I'm not sure that's very clear, my brain is all fuzzy from the workday.