I wear the Alpinestar Bionic 2 jacket:
I'm 5'8 and I have a size Medium that fits me perfect. the kidney belt wraps right around my kidney area and just at my navel, the chest zipper starts right about the navel area, and the back protection goes from my upper back just below my neck and down to just above my tail bone. All the protection sits right where it should be.
Here's the link to Alpinestars size chart and link the the Bionic Protection Jacket for BNS:
Bionic Jacket BNS size chart
Bionic Protection Jacket for BNS