Let me complement what Jim is saying. First of all, if he spends two phone calls, he gets what he needs done. More importantly the 20% rule, such as it is, isn't a rule; it's a guideline, because it comes from an officer of Parliament and is not embedded in statute. The statute actually says a “significant portion of their duties”. It's a question of what your definition of “significant” is.
I always go back to my original statement, which is that the more specificity that can be found in the law, the better.