... from what I can work out, designers take a fair bit of time to get the kites flying exactly how they want it too and then to keep the pedigree or feel right through the sizes with tweaks to suit the biggest/smallest kites ie you don't want a 7m too fast or 17m too slow. So if you get a quiver of one brand, they all will feel/fly the same no matter what size it is. Added to that, you can use one bar across your whole quiver and get exactly performances as the designer intended. I surpose that if your not happy with the over all package feel of the kite then changing kites will be necessary for different sizes.
It takes me ages to get the complete 'feel' of a kite, to learn all the nuances where it becomes one with you and I figure if you chop and change you don't learn those nuances. Mind you, by the time I think I've got it all figured out the kites usually worn out!
For me personally, I share my quiver with my family. I use the biggest with the missus on the medium size and son on the smallest and as wind picks up we shift along (and the little one said, roll over,,,,, roll over). Only problem is the son is getting big now and is using same sizes as the missus so the quiver has to get bigger ($$$$$).
Anyway... cheers for now,
Robbie