So you bought a kite that has 9 stamped on it but it turns faster than what your used to and works better in higher winds and worse in lighter wind?
Sounds like just a smaller kite to me. These days what is stamped on the side of the kite usually bears little resemblance to what the actual kite size is. and power output per brand and kite type varies greatly.
Ride the kite that feels right for the conditions and don't bother what the size on the side reads. All you have to do is change your impression of what kite to pump up on the day.
On a side note wave kites (low aspect kites) will be worse upwind and also create less power with apparent wind compared to their higher aspect brothers. It is what it is. you cant change it.
PS What is this kite you speak of?