While Jan's illustrated method is fine for "at home" quilts (there are many others, as well), if you are quilting for show, it's best to stick with a full width 4" sleeve unless you know something else is required (or permitted). In judged shows, sleeves are subject to judging...and in juried shows, you may not even get in unless you abide by sleeving requirements. The OP was specifically asking about show quilts in this instance.
Two notes on sleeve construction;
1) there is less obstruction to the rod if you sew your sleeve seam with the WRONG sides together. That puts the seam allowances on the outside of the sleeve which places them facing the backing of the quilt, never to be seen again and entirely out of the way of the rod.
2) if you fold over a ¼" twice on the short sides before stitching, a double fold, you will not have a raw edge inside the sleeve. Stitch as closely to the folded edge as you can to reduce the fabric lip. It will look neater, wash more securely, and load more smoothly over time.