You read my mind. I am having the same "problem" with my dreads as well. How much did your hair shrink? I've noticed my ones that shrunk the most are super fat on the bottom and not as much on the top. It doesn't seem like I am loosing hair so I believe it to just be that my hair doesn't want to dread up as thick as it did in the beginning.
Another thing is look at your sections and see how/if they have changed. lots of ones that have morphed over the last year that were originally small that got larger or got smaller from other sections eating hairs.
There is a section on the right side of my head that used to be huge but now it's average almost on the small side because the two next to it ate a lot of hairs and as Iseparated(didn't notice until recently) I favored giving more to the other ones rather thanpreservingthe original size.