Why put anything like that at all in writing? This kind of rule is an example of how the racing rules of sailing got so complicated. Every time there is a new rule, some people find a way to take advantage of the rule, and then you have to add clarifications and exceptions and sub-rules.

In this case the rule is not even necessary in the first place. Unless, of course, you think the PRO might be bribed by or has personal ties to some of the competitors who happen to be light-air specialists. In which case there will be a big scandal and that PRO will be banned from ever running another race and will lose his pension benefits.
Isn't it the job of the race committee to use their discretion and judgment? By putting something like that in writing and putting a number on the wind, you are just providing specific ammunition for some people to attack the race committee's "judgment" and fuel for controversy like the one on this thread.