Thinking that the sweeping crews may not have chance to feel the balance along the central line, suddenly I think of one way to practise balance is to stop at back-stop, half-slide, full-slide, with only the inside hand holding the handle, while, the outside hand holding in the air in a position symmetrical to the inside hand. It will better even with the hands-off the handle. Just an imagination, I haven't do that before, but maybe it worth a try.