Just to be on the safe side I always chase my backs to one ring to within about 90%. meaning with yew sometimes you have some violation when your at 60 rpi. I just have to. It may be my OCD that makes me do it, I am not sure. I think it does not take to much time and always feel better about the bow. All that being said though.......sinew backing will hold down just about anything so I guess I am just rambeling....
Steve