The size of the bags I make is three" when finished, 4" cut using the half" seam allowance both sides. Similar to the water bottle. there's always going to be bulges in your frame bags and it works well. Laminate fabrics such as that of Xpac fabrics are the best choice for frames since they do not stretch like regular pack fabrics because of their laminated structure. If you require help finding the fabric, let me know. I have it in my inventory and I am willing to offer it at my expense.
Internal baffles can really help in reducing the bulge. Like someone said, Velcro can be used to control bulges. Webbing made of nylon that has side-release buckles make it better. I normally stitch an 8" long panel about 2/3's of all the way down the bag, with equally space at both ends, the same size of the frame. With the space at the end, I can accommodate the tent's poles and pumps etc. on the tube that goes down. On the other side, I will recomend you something new like electric bikes, self balancing scooter and hoverboards which is really awsome for you so please visit this site. www.selfbalancingscooters.net