iv used this method for nearly 4 year with my sonic ,also works well with best kites and flexifoil with no problems ,all you need is the right amount of sand in the bag so that it does not drag or move ,the kites will just hover up and down a little at the edge of the window but aslong as the kite is on full depower, u will have know problems ,next time im out i will try to film this to show u all how to do it but it a good method ,last year i went to falmaer in lanzarote i forgot my bag and i was on my own ,so i dug a hole in the sand found a good size rock which would hold the chic loop in the ground put all the sand back in the hole then turned my kite over ,all was well ,one of the biggest things is to understand how your kite works properly ,hope this helps ,