I have same problem! My hair is 3a/b but underneath totally straight or little bit wavy after diffusing, but unfortunatelly I do not know any solution for that. I have never figured it out, it is just the way they are, I have to accept it...

but I recommend trying to diffuse your hair with head upside down )it really helps) or just pin the top layers and leave bottom layers to dry without the pressure from top hair.

Good luck!
3a/b fine, ii, normal porosity I think...

Full CG start
Growing out....again

now: chin lentgh
shoulder lentgh

Loves protein and YTC hair mask!