Chris, you are getting mixed information here, and from the information you have provided, I can understand why.
First: when you say the fired brass is "longer than the sized cases" how are you measuring this? The length of the case from the base to the end of the neck? Or are you measuring from the base to a datum line on the shoulder. (Headspace length)
Second: depending on powder/bullet combination, your fired case will be longer than your sized cases, and more important, longer than the chamber it was fired in. Keep in mind, you are not shooting a bolt-action rifle here. Measuring your fired case from yor AR does not necessarily represent chamber length. Setting your die so the shoulder only gets bumped back a little from a fired case may cause you lots of anguish.
If you have any doubts about what I have said, or need clarification on any of this, you no how to get in touch with me.