the line angle will effect whether a lead moves or not, if the tow/flow is coming directly from from the line the lead may bounce, if from the sides it can move/roll but if its coming from above( your facing into the flow/tow) with a semi slack line even a light lead can hold,as the gets line is pinned down,reducing the drag on the line.
its called up streaming( if i remeber right) may be worth you finding a feeder fishing on rivers book ,or google it