Maybe I am overthinking all this, also. Thanks.
You're not overthinking it. You're applying bolt gun methods to a semi-auto gun.
The body of the case needs to be sized back to function in the AR chamber.
If the case is a little too long in a bolt gun, the bolt won't close and you'll know you've got a problem. If the case is a little too long or the base hasn't been sized back smaller than chamber dimensions in the AR, you have a possibility of the case sticking in the chamber before it seats fully, and you can have the round fire out of battery. Then you'll know you have a BIG problem.
If you're lucky, the round won't fire, but the force of the bolt will have stuck the oversize case so tight in the chamber that you'll have to drive the live round out from the muzzle end.
Full length sizing is the only way to go for an AR. Some folks even go so far as to use small base dies for a little extra squeeze.