The triggering of an insufficient ventilation warning as described in the Standard 4.5.3 seems to be 16 L/s, but they describe that as a lower limit and there being an upper limit of 40 L/s in some cases. Am I misunderstanding something fundamental? In my first few reads of this I thought it was being described as the ventilation warning would be triggered between 16-40 and couldn't understand why there would be a floor. In reviewing the formula my understanding is that the warning is triggered in cases where the ventilation rate falls below 16 L/s which makes more sense but...

I can't find anything describing the function of the upper limit or the cases in which it applies.

In case you want a response with the Building Code referenced, see attached image.  The 16 minimum is prescribed by the code and the max 40 lets it fall into 4 or 5 bedroom homes.