okay that is the most difficult piece of the vest. this piece has a double curve. you need to leave it big, so you can bend it to the right shape before you cut it to bend well with the adjacent parts.
i recommend you study the photos of Sloan and my vests. then you'll see how the piece is supposed to role over the shoulder. leave the piece long, form the piece into shape using a heat gun. then cut to meet the front shoulder part.
Wish I had seen this thread in January! Great job
Looking great so far!
Zookone deserves all the credit for the vest though. Those are his patterns. I'm the upper arm guy
Regarding the upper arms. I've made iterations and improvements over the years. Most recently I completed the Mankind Divided suit.
I've ditched the upholstery foam covered in black fabric and now, I just cut the muscle shapes out of the craft foam and foam mats. Much simpler, easier and sturdier.
Good luck!
Looking good man!
I think you might benefit from some better reference images for the vest(s) though. The lower back is not part of the inner-vest as you have it now.
As you can see in this image, it's part of the outer armor vest.
(Note: the lowest part of this vest is not attached yet (yellow).
Hope that helps. Good luck!