How to encourage curl in straight sections of hair?

About three years ago my hair was a consistent slightly wavy 2A. Since then, it's completely transformed: parts of it are 3A, 2C, 2B, some is still 2A and I think some of it has actually gotten straighter. I love my 3A/2C sections and I wish they were over my whole head, but they're only in the middle of my hair. The top layer and bottom strands are much straighter and they look very weird next to the curls since they appear so much longer. Worse yet, the 2A top layer completely covers up the pretty ringlets in the center :( I've tried so many products for this, the central curls love them but the top and bottom sections refuse to curl up at all. Any recommendations to even out the texture?

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