The force line to the base runs through the hip and the center of gravity of the flyer. Otherwise arise very fast tilting and turning movements that are only with much experience to brake. This position should only be strived for if the flyer does no longer correct in the standing on 2 legs. For example, if standing on the straight-arm works fine.
Initially, the base should use the 2nd hand for stabilization!
He may achieve this, e.g. after he is bringing the feet of the flyer together and then grip with his free hand to the 1 leg. In particular, the ball of the thumb should be supported in order to counteract the buckling of the flyer inwards.
The one-armed balance of the base only makes sense if its forearm runs exactly along the line of force. See also Preface Topic: Muscle mechanics – force line! On the straight-arm with the lying or standing base also the shoulder must be in the force line.