To date in all the sailing I have recently been to, there has never been a big enough fleet of F18's to warrant excluding the F16's but then I tend to only go to competitions where other F16's are and that tends to be our TT's with the exception of Simons home event, where the F18's are taking no prisoners and will run over you and protest rather than take a poor race result. In those cicumstances I would rather not sail with them but then I'm a bit of a wuss ( most of the time ). Seeing 5 or 6 F18's start and then 5 - 6 F16's seems daft to me, yes on the bigger events where numbers are higher say around 20 or more, then have seperate starts, on the smaller event just lump them all together.
We've already had the conversation about the F18 drivers being over aggressive a$$holes so I won't revisit that. But, I still find it odd you want to sail with those kind of people.
One more thing... if the F16 fleet gets the numbers you want your fleet will be the home of over aggressive a$$holes, that's just how it works.