What's happening Barbara is that some of the fluff is bypassing the filter because its escaping through the seal between the drum and the door front...all dryers do this to some degree and the older the machine the worse it is. In fact if you were to open the machine up you'd see loads of fluff inside the casing too. There isn't an optimum height for the ducting, but the shorter the better. It shouldn't have dips in the pipe either because condensed water can collect there.
John, July 2009
