Note that in example "A" the CB is always coming off adjacent rails which maintains running english and if not hit with exact speed control could rebound and run off the head rail. Where as example "B" has the CB going from long rail to long rail and thereby reversing and killing the CB as it approaches the head rail.
After seeing pretty much everyone breaking from B I started to think that it must be a rule. I've actually never done an opening break from B so I can't really comment on better or worse results.