I find that when natural hair is straightened..
It has to be sort of weighed down a bit for it to last.
Usually the day after its been wrapped, it holds better and some of the "slick" is gone.
I think maybe if you use something with a creamier consistency before you had blow-dried or air-dried. Then use something with an "oily" consistency before flat-ironing..
It might hold better, and you'll be doubling your heat protectant too. :)
I'm not that big on straightening anymore, but that's what I would do.
But maybe you need to use another product.
When I used IC's products, my hair didn't turn out so great.