When the marshaller wants the helicopter to stop, or hover, he gives the Hover signal.
Hovering height (not altitude) is normally decided by the pilot, and is typically four to six feet wheel/skid height. If the marshaller wants a higher hover for some reason, he gives the appropriate signal. It's no big issue.
I must stress the precise positions and orientation of hands, in particular, are most important, much more so than when marshalling aeroplanes. It is very easy to confuse the signals for moving forwards, backwards, and upwards, if the marshaller is not very good.
My advice is to find a pilot as pedantic as I am, if you can, and ask him before the bar fills up too much.