I'm Traddy and these are my dreads...!
yeah you dont really have to sleep with anything on your head. the tshirt is normally used to prevent loose hairs from forming and to stop congos, but if you're nto having a problem with either i wouldnt worry about it, and even if ya did id say dont sweat it, nothing wrong with loose hair, i got tons of it. and i wouldnt worry about the thinning of the ones you're talkin bout. it probably is just the weight of the dreads where as before they were curling in and dreadding in big thick clumps cause of your curly hair (i know cause from what i can tell we have very similar hair types. so yeah its probably just the weight of the dreads pulling them a lil straighter as the new growth dreads. i gotta say though ive never seen quite so much visible scalp at the top. but that might be just because of your very even part and the lack of loose hair. mine are like all over the place at the top. oh also on the note of the thin dreads, everyone has sections of their hair where its thinner. mine's on the sides and everyones is a little thinner on the edges i think. bothers me alot my side dreads are the thinnest. anyway hope my tips were helpful