that's normal with a big kite. they are too slow to boost you up in the sky, therefore they can carry you longer through the air due to the large surface area. it is like a parachute. if you have a smaller kite, it turns faster and pulls you up more due to its speed. the highest jumps I did were with an ARX 7.5. My 15.5 has a longer airtime once up flying. But the 7.5 kicks me up and brings me down fast since the surface area has only 7.5 mÃ‚Â² which is not enough for my weight to make me fly longer.
So don't worry, it is not you!