It’s rare to find more than a few feet of depth around an island, so fishing shallow gives me no advantage. Instead, I try and set the waggler so that the hookbait just touches the bottom, with no shot down the line on the rig for a natural fall of the bait.
That way, most of my bites happen within seconds of the float hitting the water. Only on windy days will I set the waggler slightly deeper to deal with any tow created. Flicking the rod-tip sharply to sink the line also helps on windy days.