"Drop figure to floor" script works fine so long as the figure does not leave the floor during the animation, but jumps or parts of a fast run where both feet might leave the ground will be adversely affected. In such cases, you can use another method. Open the graph editor for the hip's Y translation, expand the range so that you can see all frames, click and drag above or below the line of keyframes, high-lighted /selected frames turn black. Hold down Ctrl and drag the keyframes up to the required level.