right. Time for a constructive answer... Trainer kites* and beach practice won't help you with this as once you are on the board moving the kite becomes dynamic. The reason why kiting works is because once you dive the kite and "move" the kite will never be able to leave the powerzone to the edge as your board keeps "catching" up with the edge of the window. At least once you have speed.
Your problem is that you don't generate enough power when you start so your board is too slow and the kite overtakes you and moves to the edge. There is two things you can do.
a) Make yourself go faster
( b) buy yourself a bit more time to gather speed which leads to a) )
c) make the kite go slower to the edge.
So a) is basically to give the kite a much sharper dive into the powerzone. Some people literally dive the kite from 12 to 6 o clock in light wind. As a result you get more power, more speed and the kite also doesnt move as much to the edge as it dives more down to the horizon. Probably only a good idea if you are confident as you can easily do a superman. If you try this makes sure to really kick your front leg up to the sky as you get lifted out of the water and then put like all your weight on your back leg. (so the nose of the board doesnt get buried in the water).
To do b) you sort of move the kite to 10 o clock and then dive it sort of at medium speed up to 11/12 and then back down to 2 o clock or just go directly through the powerzone. As the kite takes a bit longer now to move from left to the right you have a bit more time to gather speed. Can also lead you to doing a superman.....
The first some people also call 2 stroke start. If you start to your right you move the kite to like 10 o clock. Move it up to 1130. This will lift you out of the water and turn you in the wrong direction a bit ( perfect for going downwind
, especially if your board always points too much upwind) and then your second powerstroke from 1130 to ~2 or 3 will get you going.
c) So once you are up on the board you need to IMMEDIATLEY steer the kite sharp up and then sort of sharp down again. By going up and down (a sine shape with high amplitude) the kite essentially can't really move to the edge and you can gather speed. Do this maybe 3 times (Normal downstroke, up on the board, sharp up, sharp down, sharp up and then hold at 2 o clock) you should have enough speed. Should the kite move to the edge of the zone just sine it up and down. Should your board go too fast now and the lines go slack or the kite goes to 12 as you now overtake the kite either steer it towards 3 o clock (bad idea as this will make you even faster) or edge the board and go upwind for a few seconds and push the bar out.
*unless you go to i.e. a football field and practice on a skateboard if theres plenty of wind.
