my bottom layer of hair is like this too! no matter how much product I put and how much I try to scrunch or twist it around my fingers, it's just lifeless! at least it's my bottom layer underneath everything so it's not too noticeable!
My canopy is very curly but the underneath barely has any waves at all. I diffuse my hair while scrunching. When it is almost dry, I duck-bill about 8-10 loose scrunches up all over my head and leave it for anywhere from 15 minuites to up to 1 hour. I also use Biosilk RHG, which is serious business when it comes to holding curls. Growing out my top layers (which I am still doing) has --obviously -- helped give my hair a more overall uniform look (the curly top falls over the straight bottom).