LOL, San, you are so funny. Actually you (and Tanya too!) have the legs and figure to pull these off, if you wanted. The trick is to get sleek boots - not something like this, which I think are just awful:
http://www.freepeople.com/inde.....-_-Primary
They remind me of waders! For fishing!
If the boots are sleek (yes, even in the knee area), you get one long lean line. I think this is why having that slit in the back of the knee helps. It enables you to have a more form-fitting boot around the knee, while still being able to bend the knee.
And yes, I think showing a bit more thigh helps give some shape too, but more importantly, creates balance. Not necessarily a micro-mini, but one that hits halfway down the thigh? If you go too long, you're covering up the top of the boot. I guess it's just like when you wear regular boots with a skirt - you want a bit of space between the top of the boot and your skirt. Possibly it's one of those things you have to play around with to get it right.