Hi there. I'm uniquely able to assist with this question, being as I was a GML for my 501st Legion Garrison for a few years and have been the XO of the Pathfinders Detachment for the past 3.
Here is the example from the CRL:
Now, the sleeves should really be a bit longer here, but this is the general idea. The ribbing is usually spaced about an inch apart. The reason I've included the second photo is because the original flak vests made for ROTJ were made in the style of a raglan sleeved shirt, seen below...
You'll notice that there is no seam at the shoulder, but instead, it starts at the collar. There are patterns out there for making raglan sleeved shirts, so if you want this look, it's definitely possible.
To the OP, I'm not exactly sure what they meant by "elongated sleeve". I know that when I help scouts with their flak vests, the shoulder armour usually ends about an inch above the sleeve opening.