Try getting a silk or satin scrungies. And most of all dont pull the bun band too tight. Try doing looser ones. Dont sleep with a tight bun or ponytail either. Moisturize the area wear the band will be and try putting moisturizer on the band too HYH
I saw a youtube video on "How to Wrap Your Hair With a Scarf" from SalonCabelo. She says in the video that we should change the direction of our wrap because it can cause one side to grow slower than the other or cause one side to get thinner than the other.
The best advice I got from LadyEsquire almost a year ago on Fotki was to texlax the hairline. It's how I kept my length in my nape. As you can see I had some old Allan Payne chest hair looking taco meat thing going on back there due to overprocessing and picking at my nape all the time. The pics are over 10 months. I've retained my edges the same way. I never relax my hairline straight. They are just too fine and take too much manipulation for that.