Damage and length probably contribute a lot. Crown/canopy have a tendency to be less curly because it's the hair that's most exposed to the elements (translate drier and more damaged.) Hair weight also pulls out curl.
If your ends are dry/damaged--a haircut is in order. Getting more layers will help it curl better across the board.
Your drying technique may also help. Water weight also pulls out curl. You can try plopping (if you don't), scrunching out water with a curl towel and diffusing to set the curl.
3a (Corkicelli), highlighted, fine, low porosity
modified CG, since April '07
CG since 3/11/08
HGs: Curly Kinks Satin Roots, Curlycue ReNew and Coil Jam; homemade FSG and okra gel; soap bars; DM MiraCurls Curling Gelly; UFD Curly Magic; Shescentit LIs; Sevi conditioners; Botanical Spirits Puree, CJ Repair Me