I know this isn't going to answer your questions and I'm sorry about that but you will have to decide what kind of back quiver works for you and what you want it to do for you. I like a medium size quiver for general 3D shoots and roving the back yard with judos. I also like a quiver that is soft and kinda floppy so it contours to my back and keeps the arrow from rattling so much (this really helps when you are putting the stalk on a tree rat). I'm not sure the size of your fletch will make a lot of difference in the size decision as those ends of your arrows won't be inside the quiver.
I have a friend I shoot with that like a hard tubed quiver the is rather large. Think 6" PVC pipe with a strap on it. He says that since he can't see the quiver opening behind his back he just has to get them close and drop and usually the arrow fall into the quiver.
I started making quivers of all kinds and it really isn't hard to make a functional quiver. The hard part is making it really pretty. And you most likely have all the tools you need to make a functional quiver, razor knife, 2 penny nail and a scrap board for poking holes in the leather with the nail. There are several good build alongs on the How-to and build along forums here.