well any naish users may be able to better reaply to this but from what is read the boxer is not exactly a jumping machine just a realy good al round performer. what are the other people using that you are comparing you self to, if they are on high aspects then it is not all that supprising that you are not geting as much verticle lift as them, it could also be your board, what is the board like flexi, stiff, lenght etc.... what lenght lines are you using???
as far as what you should be doing, in theory any way, aproach the jump at a fairly high speed, genraly the faster you ride the higher you will jump, if however you are very overpowered you will not get as high a jump as if you where "perfictly" powered. so aproach the jump fast and the same with the kite the faster you redirect the kite the higher you should get, try to have the kite between 11 and 12 and send it to the oposite side but probably not as far or you will tend to come of you axis, there is also a difficult balance to master as far as power in the kite when jumping, if you fully power up the kite before sending it wil slow the kites traviling through the air, reducing the aparant wind and giving you a more horizontal jump, but at the same time if you fully depower you will simply not get the hieght you want, you have to balance it, not to much depower but at the same time dont power the kite up to much , there is a very fine balance.
as far as jumping toward the kite i really dont think in my opinion it is nessasery to "throw" ur self toward the kite this may actualy hinder you in gettin maximum height, i think that depending on the wind strenght obviously, you should simply edge untill your kite rips you of the water. also jumping of a wave will vastly increase you height. things that may help without having to buy a new board or invest in the latest hig aspect jumping monster are; bigger fins to help hold an edge, or widen your stance on your board, i.e. move you foot straps out as far as possible, if possible. and iff your lines are shorter than 25 meters get longer lines and if they are longer than 30 meters get some shorter ones, the longer the lines the more hang you will get, the shorter the more height, i think 27 meters is about right. hope this helps and hope its all correct apoligies is im wrong
just enjoy it.