I think IA Girl had a post that worked out the sun damage math something like this.
Suppose your hair grows about 1/2 an inch a month.
Suppose your hair lasts about 6 years, before it falls out and gets replaced.
Suppose your hair is exposed to the sun for 30 minutes a week.
That equals almost 10,000 hours of sun damage!
Of course, it's the hair on top (the canopy) that takes most of that damage. The rest of your hair is protected by that hair

So, it's going to take a while to help your canopy catch up to the underneath hair.
Also, layers may help. The weight of the length of the hair may be pulling curls out.
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Hair: Very fine, normal porous (Finally! Yay!), normal elasticity, loves high dew points.
Daily: Nature's Gate Tea Tree shampoo, GVP CB, Cure Care conditioner, aloe vera gel, Jessicurls products, Spiral Solutions products.
Monthly: Henna
As needed: John Masters Organics Sea Mist
HG Product: BioSilk Rock Hard Gelee (aka BRHG. It even has HG in the name!)
Last perm: 12/10/10
CG since: 3/9/12
Last haircut: 4/17/12
Gossamer Fringe (my blog)