I'm wondering if the issue with your bangs is not product build up but actually sebum? Bangs can be a b!+(# lol. Maybe it would help to list what conditioner you use for co-washing, and what products you use for styling, then we can look at the ingredients and have some more specific information to go on. The itchies and white flakes could also potentially be a reaction to a particular ingredient that is causing your scalp to be dry.
2a/b, high porosity, fine strands, average density, just about shoulder blade length

My hair loves moisture!

currently mod-cg , using low-poo and not totally cone-free yet. I'll get there though!