I've always thought that just because I relaxed my hair I wouldn't have any shrinkage. It's definitely not as dramatic as natural hair's shrinkage but it's definitely there. I noticed it more once I started air drying instead of flat ironing.
Case in point. Check out my little shrinkage. And by the way, I am so dangerously close to BSL and I am loving it.
I am also loving the thickness of my hair right now. In that picture I was only 4 days post relaxer after a cowash and air dry.