Yeah, there seems to be exceptions to the rule when it comes to phenotype variations. I had my Blueberry Punch which is Indica dom grow nearly 2' high(on the first run from seed) and didn't show any sign of sexxing(about 6weeks) and then I went ahead and flipped them. Within a week They were all busting out with sex parts.
I think the phenotype combined with environmental factors really affect how this occurs timing wise. There are really a lot of variables that can affect the plant. I have learned soo much in the last 2 years of serious growing, and I am still learning stuff all the time.
Fizzgig, If they are that far along you could flip them if you want to before they get any taller. IMO it wouldn't hurt to do that, and they probably would show sex pretty quick after that. Some peeps here would say that flipping them too early causes them unnecessary stress, but this close I don't think it will hurt.
The only problem with flipping before they are suredly sexxed is if you want to take clones from them. It's a pain to have a bunch of clones that haven't sexxed yet and then find out that half of them are males a couple weeks later. But there are ways to get around it if yer prepared for it. Ultimately its simpler if you intend to clone yer plants to let them fully mature.
I probably sound like I am contradicting myself but I try to show both sides of the arguement whenever I explain things.