its about preloading the actuator to control when the waste gate opens or how long it stays shut. on old school turbo motors like RS Turbo's this is a cheap method of achieving more boost....its also the reason why eventually they blow up.
you shouldn't adjust yours on the
ibiza, its not clever really when boost is controlled electronically, especially if your unsure on what you're doing in the first place.there are reasons why you would do slightly, but not on standard turbo