i agree with missy and everyone else, but if thats the approach you've been taking and its not helping, i was going to suggest leaning your torso forward, while not dropping the chest, just a slight pitch forward, in order to get the feel and develop the height. People' limbs are proportioned all different, making some things more anatomically difficult for individuals, regardless of flexiblity and abilty. The take off is from a stationary plie and not at all like the feel of a traveling grande jete. youve gotta have a solid plie and push from the earth like a volcanic eruption. Also play around with jumping with the arms in a V, not worrying about your fingers touching your toes, but just concentrating on your toes reaching the clouds. Especially in cheerleading theres usually this elaborate prep. with the arms going up...down..around windmill style,...and touch toes... when you learn toe touches that way, your body's is fooled that the momentum of your arms is what instigates the jump, and thats not nessesarily so, sure the aid some, but the key is the PLIE. (try doing it keeping the arms down, its even more difficult,) i guess what im saying is experiment with small adjustments, untill you've disected the jump, and figure out for yourself, keeping all the technique in mind, what its gonna take.