You are less likely to need to thin your yew sapwood on a warbow, because its dimensions are larger than a regular weight bow.
It comes down to what you are dealing with on the stave you are working.
At 1/2" you can thin the sapwood, to 1/4"- 5/16". Unless y0u are dealing with low ring count yew, I wouldn't bother to slavishly one ring. Yew doesn't need it, and Medieval/Renaissance bowyers didn't bother follow one ring with yew either. IThat being said, you still need to follow the natural run of the grain.